Could be a number of things causing this, or could just be a bug in the latest beta iteration. So if you'll bear with me we'll go through some diagnostics. A lot of these are unlikely to be causing the problem, though for the minimum time/effort it's worth checking anyway.
1) Check HDD SMART data to see if the hard-drive's corrupted.
You can do this by downloading SMART Utility here. Anything other than 'Passed' means you need to replace your hard-drive
2) If that comes out clean, open Disk Utility and click 'Verify Disk'. Make sure you verify the OS partition (bottom of the two 'Macintosh HD' listed). If you have red writing, it needs to be repaired. Green writing or no writing means it's OK. Please quote this if it's red and you need assistance repairing.
3) If Disk Utility comes out clean, try restarting with the option 'Reopen windows when logging back in'
disabled.
4) If that hasn't fixed the issue, try a permissions repair and restart.
5) Reset PRAM/SMC.
6) If you're still having the issue after this then I'd probably submit a bug report.
Also, could you confirm the following:
- Does the issue happen with USB mice/keyboards, or is it just the internal devices?
- What model of MacBook do you have?
Speak soon.
