The BAS805 installer should have registered the file automatically but the error message seems to suggest it hasn't been registered. One thing you can try is to register the file manually. From the Start -> Run menu or an 'MS-DOS command prompt' enter ( exactly as shown, double quotes and full paths ) ...
C:\Windows\System32\RegSvr32 "C:\Windows\System32\isDigitalLibrary.ocx"
Do you recall which version of Programming Editor you previously had installed before upgrading to 5.3.1 ? Also which Windows OS are you using, 32 or 64-bits ?