I've experienced strange bug with updating from stable to beta version. I use MultiUpdate for update and after update completed MC doesn't start with error message which complain for broken configuration. I copied MC from C: drive to D: drive and update installed without any problem, afterwards MC start as usual. Very interesting moment: MC updated to beta flawless on other PC and on my USB stick. All my MC copies is portable versions.
All my PC runs Windows 8.1.