After progressing in certain quest-lines, I noticed that I can no longer access The Castle. Every time I attempt to my game crashes and I receive a 'Pure Virtual Function Call Error' with 'r6025'. All drivers are up to date and my game was reinstalled but to no avail. I don't know exactly what quest caused this but my really old saves don't have this problem.

Did you search Google for that error? Lots of results, possibly linked to C++ Redistributable.