i have had the same problems with maya 2011 on a mac running 10.7.5
three times since dec 2012 my license has completely broken.
i have been working on big scenes admittedly one ongoing one is 400MB.
getting new authentification codes off autodesk is a titanic struggle. i have to angrily insist that it is just me, one person working on the very same desktop machine. sometimes when i have received new authentification codes they have not worked.
last time i had to perform a completely fresh reinstall on a new hard drive to get an authentification code to work.
i spent a fortune on this software over the years and i find it's disgraceful that it breaks in this manner - disgraceful too that i get treated like a criminal.
i am now looking at upgrading to maya 2013 and some of the comments here fill me with dread as i read users are facing the same problems with more recent versions of the software.
AUTODESK SORT THIS OUT - IT IS A DISGRACE.