The Agile Platform Community Edition 4.2 is probably trying to reuse the same database catalog previously used by the Agile Platform Community Edition 5.0. This is the expected behavior, however, the Agile Platform in general doesn't allow the downgrade of the OutSystems databse catalog, due to possible data and metadata inconsistencies.
So, you have 2 choices:
I suggest you identify which extensions are not being upgraded, possibly due to the breaking changes, and post them here. We will give you a hand in upgrading them. :)
Miguel Simões João