There are a number of ways to address this issue, as described below.
First option to fix the error 'Could not open file. Unrecognized database format':
Go to the Ledger File Location.
Take a copy of the Ledger.
Paste the copy into the same folder. This will save a copy as Ledger Name - Copy.
Right-click on the Ledger copy and select Compress to Zip file.
Extract the Ledger copy from the Compressed Zip file.
Merge this file into XPA. For details, see XPA: Merge a file into XPA.
If no error occurs, the issue is resolved.
Second option to fix the error 'Could not open file. Unrecognized database format':
Open the Advance Applications list.
Go to Xcede Professional Accounting.
Open Administration Tool.
Ensure you have the correct practice selected, then search for the ledger name containing the error.
Locate the Ledger in the list.
Right-click on the Ledger and select Compact/repair XPA file.
Open the Ledger in XPA to test that the error no longer occurs.
Third option to fix the error 'Could not open file. Unrecognized database format':
Request your IT team to restore a copy from a previous backup prior to this issue.