Unrecognized database format
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
- In 2 of the 3 accdb files that can be opened, the error occurred only when trying to access certain tables.
- In another file that can also be opened, the error poped up at a different moment, when trying to open certain forms and reports.
- 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:
Error when opening a table
When trying to open a table the error Unrecognized database format is displayed
The database can be opened.
When trying to open some tables, even in design view, the error pops up:
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 |
|
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 |
|
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.
The database can be opened.
Forms and reports, when you open them, raise the error:
Queries, when you try to open or edit them, return this error:
However, forms and reports can be opened in Design view without incidences.
-
When we try to open a form or report, one of these 2 errors is displayed:
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 |
|
Recovery Methods |
|
Cannot open database
Attempting to open the accdb file displays error Unrecognized database format.
You try to open the accdb file.
-
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 | |
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 | |
Recovery Methods |
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 | |
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 | |
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.
