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Unrecognized database format

Microsoft Access Error: Unrecognized database format

David Cimadevilla

Nov 12, 2019

How I repaired 9 MS Access files that returned the error "Unrecognized database format". An article in the series "How I repaired 28 corrupt databases".

During the preparation of the How I repaired 28 corrupt databases research project, I purposely damaged 28 Microsoft Access files in different parts of their internal structure.

The modifications were carefully designed to affect specific objects in the database. The goal was to get a good sample of the different errors that can be seen in a damaged Microsoft Access database.

Of the 28 files, only 9 of them showed the error that is the subject of this article. Although all of them returned the same error, Unrecognized database format, the symptoms and results were different in each case:

When the error occurred

  1. In 2 of the 3 accdb files that can be opened, the error occurred only when trying to access certain tables.
  2. In another file that can also be opened, the error poped up at a different moment, when trying to open certain forms and reports.
  3. The other 6 files could not be opened at all.

How I repaired them

  • 2 of them were completely unrecoverable.
  • I was able to repair 3 using Compact and Repair.
  • In 4 cases I needed to use a data recovery tool.

How much information was I able to recover?

  • In 2 cases nothing could be recovered.
  • In some cases, only the text fields could be recovered from the tables.
  • In others, tables, forms and reports lost their names although their contents were fully recovered.
  • In others, part of the objects were lost.
  • In others, all was recovered.

When is the error displayed?

If you want to see cases similar to yours, you will need to note the moment when the error is shown.

I have classified the 9 accdb files according to when the error is displayed:

When opening a table

  • corrupt-system-relationships-def.accdb: Corrupt inter-table relationship container.

  • corrupt-customers-def.accdb: Corrupt table definition.

When opening a form or report

  • corrupt-system-queries-def.accdb: Corrupt query container.

The database cannot be opened

  • empty.accdb: Empty file.

  • zero-overwrite-whole.accdb: All data erased.

  • zero-overwrite-beginning-400K.accdb: Beginning data erased.

  • corrupt-header.accdb: Corrupt header.

  • corrupt-index-page.accdb: Partially damaged index.

  • corrupt-objects-def.accdb: Corrupt object storage.

Error when opening a table

When trying to open a table the error Unrecognized database format is displayed
  1. The database can be opened.

  2. When trying to open some tables, even in design view, the error pops up:

    Microsoft Access error: Unrecognized database format
  3. After accepting the error, the table doesn't open.

Files

In these 2 files the error appears when opening a table.

corrupt-system-relationships-def.accdb

File

1/2

Damage

The data structure that stores the relationships between tables is damaged.

Prognosis

Good.

How to identify

  1. No table can be opened, not even in "Design View".

  2. The Database Tools | Relationships window cannot be opened because it returns the error:

Microsoft Access error: Unrecognized database format

Recovery methods

Using Compact and Repair the problem is solved although all relationships between tables are lost.

corrupt-customers-def.accdb

File

2/2

Damage

The definition of some tables is damaged. The records are still in the file. However, there is no way to decode them, nor to recover them.

How to identify

  1. Some tables cannot be opened, not even in "Design View".

  2. The Database Tools | Relationships window can be opened but appears empty.

Prognosis

Bad for the affected tables.

Recovery Methods

Use a data recovery tool capable of regenerate or import table definitions.

Warning!:

Tables

If you use Compact and Repair, the affected tables will be deleted. It is important that you make a backup before trying this method.

Error when opening a form or report.

When trying to open a form or report the error Unrecognized database format is displayed.
  1. The database can be opened.

  2. Forms and reports, when you open them, raise the error:

    Microsoft Access error: Unrecognized database format
  3. Queries, when you try to open or edit them, return this error:

    Microsoft Access error: Cannot open database
  4. However, forms and reports can be opened in Design view without incidences.

  5. When we try to open a form or report, one of these 2 errors is displayed:

    Microsoft Access Error: Cannot open database
    Microsoft Access error: Unrecognized database format

File

This is the only file that shows the error when opening a form or report.

corrupt-system-queries-def.accdb

File

1/1

Damage

The data structure where queries are stored is corrupted. Forms and reports are also affected because Access internally uses queries to open them.

Prognosis

Good.

How to identify

  1. No query can be opened, not even in "Design" view.

  2. Opening forms or reports generates one of these 2 errors:

    Microsoft Access error: Cannot open database
    Microsoft Access error: Unrecognized database format

Recovery Methods

  1. Using Compact and Repair repairs the accdb file but all queries are lost, which will affect the forms and reports linked to the query.

  2. A data recovery tool capable of recover orphan objects will be able to recover the entire file, including queries.

Cannot open database

Attempting to open the accdb file displays error Unrecognized database format.
  1. You try to open the accdb file.

  2. Microsoft Access error: Unrecognized database format
  3. The file won't open.

Common features

Common features when the file cannot be opened.
  • Probably the accdb file is damaged in the first KBs of the file.
  • You will not be able to use the tool Compact and Repair Database because Access will return the same error if you try it.
  • You will not be able to use the import all objects from a damaged file technique because Access will return the same error if you try it.
  • There is a possibility that all data has been lost.
  • The header of the file, the database's index of objects, or the storage of objects, is affected.
  • Most Access repair utilities won't be able to recover tables unless they include specific functions for recovery of orphaned objects.

Files

None of these files can be opened. They all show the error "Unrecognized database format".

empty.accdb

File

1/6

Damage

The file is 0 bytes in size or too small.

How to identify

Check the file size.

Recovery Methods

Irrecoverable.

Although it is obvious, you may have overlooked it.

zero-overwrite-whole.accdb

File

2/6

Damage

All original data in the accdb file has been replaced with zeros or junk data.

How to identify

Inspect the contents of the file with a hexadecimal viewer.

Recovery Methods

Irrecoverable.

Similar to the previous one, but here the size does not reveal the problem.

zero-overwrite-beginning-400K.accdb

File

3/6

Damage

The initial data in the accdb file has been overwritten with zeros or junk data.

How to identify

Inspect the contents of the file with a hexadecimal viewer.

Recovery Methods

Data recovery tool.

Prognosis

Serious.

Recoverable elements:

Tables

Probable loss of tables due to the loss of their definitions.

Only tools capable of regenerating or importing the definition of the tables will be able to recover this type of table.

Table definitions, which contain the characteristics of each field such as its name and type, are usually found at the beginning of the file.

A definition could also be in other areas of the accdb file, but only if the table design has been modified recently and the database has not been compacted afterwards.

Forms, Reports and Visual Basic

Probable loss of all of them. Only recoverable with tools capable of recover orphaned objects.

Macros and queries

Probable loss of all of them.

corrupt-header.accdb

File

4/6

Damage

The first bytes of the file have been overwritten with zeros or junk data.

How to identify

Check if header is damaged.

Recovery Methods

Data recovery tool.

corrupt-index-page.accdb

File

5/6

Damage

The index containing the list of tables and other objects in the database is damaged.

How to identify

You will need to preview it with a data recovery tool capable of recovering orphaned objects. You will see that the tables and other objects have lost their name.

Recovery Methods

Data recovery tool.

Prognosis

Variable

Recoverable elements:

Tables

Affected tables will lose their name, but their contents are usually recoverable. Some tools cannot recover tables that have lost their name.

Macros and queries

Affected objects will lose their name.

Forms and reports

Affected objects will lose their name.

Visual Basic

The modules are fully recovered. The VBA of forms and reports would be separated from its object if the object name is lost.

corrupt-objects-def.accdb

File

6/6

Damage

The data container where forms, reports, macros and Visual Basic are stored has been damaged.

How to identify

Use the preview of a data recovery tool able to report the state of the objects.

In the case of AccessFIX, a damaged object is always marked with a yellow warning. In other utilities it is not possible to distinguish between damaged and valid objects.

Recovery Methods

Data recovery tool.

Prognosis

Variable

Recoverable elements:

Tables

This damage does not affect tables.

Macros and queries

Affected objects will be lost.

Forms, Reports and Visual Basic

Sometimes it is possible to recover these objects if the recovery tool can recover orphaned objects.

Note: Some tools display the name of objects without warning that they are empty of content.

Other cases

It is possible that none of the above examples will be an exact fit for your case. Although I've tried to collect examples of all kinds of damage, a file could be affected by several failures at once, or be damaged in an unknown way.

However, the variety of examples is sufficient to get an idea of the nature of this particular error, to know how to identify the different cases, and to anticipate what results can be expected after a data recovery operation.

If you can't repair the database yourself, or if you lose valuable information in doing so, you can use a data recovery tool for better results.

There is more information about corrupted Access files at ACCDB Crash Help.