Bentley View V12 + dwg

Hello all

I switched from Bentley view V8 to the Bentley view Connect Edition v12. This version does not handle many dwg's anymore. Even older files that worked without problems with the V8 version can no longer be opened with the V12 version. Only if I create a small file with few elements, I can view it with V12. Does anyone have an idea what to do?

Thanks for help

Claus