Go to IIS Manager and check .NET Framework version for the app pool that is assigned to your FileVista instance.
In older versions, this may be .NET 2.0, for the new version you should change it to .NET 4.0.
Also make sure it’s set to Integrated pipeline mode (not Classic pipeline mode)
If your existing version was using FileVista.mdb (Access Database) and not FileVista.vdb4 as the database (can be seen under App_Data subfolder) note that MS Access DB driver needs the app pool to be 32-bit. As you were running your old version and it was working, this is probably already set as 32-bit. If not you can temporarily set to 32-bit for the update.
Configure IIS to run in 32-bit mode as explained below. This way, you will be able to use the default Microsoft Access database.
Windows Server 2008 64-bit:
On IIS 7, there's an option to run applications in 32-bit mode. Open the Advanced Settings of the specific application pool that FileVista is running under and set the Enable 32-bit Applications option to true.
Windows Server 2003 64-bit:
To enable IIS 6.0 to run 32-bit applications:
1. Open a command prompt and navigate to the %systemdrive%\Inetpub\AdminScripts directory.
2. Type the following command and press Enter:
cscript.exe adsutil.vbs set W3SVC/AppPools/Enable32BitAppOnWin64 “true”
3. Restart IIS by using the iisreset command from the command-line.
After the update you can revert the setting because it will no more use MS Acccess and so doesn’t need 32-bit, it’s better to run it on 64-bit for new versions.