If you are still able to access the cube, either from SSMS or BIDS, try a full process to rebuild the structures.
Otherwise, either rebuild the whole thing from scratch or contact Microsoft CSS to debug the internal errors.
I might be able to give a better answer if you include more details.
It would be interesting to know whether the cube uses MOLAP, ROLAP, or HOLAP storage, for example, and to see more of the error details, but there you go.