I'm not sure that this will help, but there was another (not checked as resolved) thread https://community.esri.com/thread/164974
that at suggested trying a smaller geographic extent...have you tried that? Also, make sure they are in the same coordinate/reference system and extent.
I knwo now back in the 9.4 (turned into 10.1) days, we could not validate our topology no matter how we "broke it down", but I don't remember if gave a code or just crashed. That did have to do with the size of the data OR possibly the extent east/west (over the 180), even if we weren't validating over the line. We could do about 95% (different extents, different order, etc.) but the last portion would not work. That was fixed before the 10.1 release. We were using ArcSDE SQL.
Are te you using Enterprise SDE or a a fgdb or personal? Maybe you are hitting a limit? I think topology checking produces a lot of data behind the scenes.