As the development efforts start moving over to CM10.2 and maybe CM11, Cyanogenmod 10.1 is being closed off. The venerable Samsung SII GT9100 is now has a Release Candidate. This is almost unthinkable, considering the lack of graphics drivers. Head over now to pick up RC2. Avoid RC1 as it has a deep sleep problem.
If you are running the CM10.1 nightlies, you might want to make sure your build is not too far ahead. RC are usually several revisions behind. If you flash a RC over a nightly that is very much newer, strange things happen. The best way to prevent this is to wipe the system partition or downgrade the nightly, possibly requiring a reset.