One of the following error variations appears when trying to open the mode:
CONNECT Edition: "Database format not recognized or read-only. It could not be opened."
FlowMaster: Unrecognized database format "C:\Users\<User name for the computer>\AppData\Local\Temp\Bentley\<project name>.fm8.mdb.$$$"
Older WaterCAD or WaterGEMS: "Unrecognized database format"
For .SQLITE based products/versions (where the model file is a .WTG.SQLITE or .STSW.SQLITE and not a .MDB), download and install a SQLITE viewer such as SQLITE Expert Personal and try opening the .SQLITE file. If it immediately indicates that the file cannot be opened (for example "malformed database schema"), please try to restore your backup files using the wiki found here .
For .MDB-based products (where the model file is a .MDB and not a .SQLITE), open Microsoft Access and use the compact and repair tool in order to repair the database. If that doesn't work or if Access itself immediately indicates it cannot read the file, please try to restore your backup files using the wiki found here .
If you are still having trouble after that please contact technical support by submitting a service request and the Development team can attempt to repair the corruption.