Some organizations may find that after a recent refreshed of a staging environment from production. The staging environment can not load some forms although it works in production. You may also try to reloading the .dlls that would refer to the issue, compared the data forms and permissions etc., and it all matches production, yet they still wont load in your non-prod environment.
One thing to confirm is that the probing path is NOT commented out on the web.config file.
For Background: By default the Blackbaud CRM application looks within the bbappfx\vroot\bin folder for its server-side assemblies. Your custom server-side assemblies should reside within the bbappfx\vroot\bin\custom folder.
As a best practice, you should separate customization assembly files from standard assembly files. You can set in the web.config to prompt the application to look for folders named “custom” for customization assemblies.
To enable this: 1. Open the bbappfx\vroot\bin folder in your installation directory and add a "custom" folder. 2. Go back to the bbappfx\vroot folder and open the web.config file. 3. Look for the following line that is commented out near the top of the file: Un-comment <!--<probing privatePath="bin\custom" />--> and save the file. 4. The application now searches in bbappfx\vroot\bin\custom for custom server-side assembly files.