Getting the “unknown database format” error when trying to run an app that is built with the Microsoft Access 97 database MDB? The likely chances are you recently updated your computer to the latest Windows 10 January 2019 Update which appears to have an issue with the Access 97 databases.

The problem is not limited to Windows 10 alone, users report that all versions of Windows which received the update on January 8th, 2019 are affected by the problem.

Thankfully, the fix is simple. You need to download an older version of the msrd3x40.dll file and replace it with the new version released with the January update.

→ Download msrd3x40.dll v4.00.9801.5

How to fix “unknown database format” error after Windows update

  1. Download the version 4.00.9801.5 of the msrd3x40.dll file to your computer from the link above.
  2. Unzip the .zip file, then from the extracted data right-click on msrd3x40.dll and select Copy.
  3. Install msrd3x40.dll file:
    • On 32-bit system: Go to C:WindowsSystem32 folder and press Ctrl + V to paste the msrd3x40.dll file you copied in step above. Select Replace the file in the destination option when asked.
    • On 64-bit system: Go to C:WindowsSysWOW64 folder and press Ctrl + V to paste the msrd3x40.dll file. Select Replace the file in the destination option when asked.

That’s it. Replacing the msrd3x40.dll file to an older version should resolve the problem. If need be, do restart your PC as well after replacing the file.