I was about to post asking if anyone knows of this error in Maya and knows of a fix, but instead I 'Googled' it. If ever you get this error, simply do the following; Windows - Settings & Preferences > Preferences. The find the 'Undo' tab on the left hand side, there you can find the On and Off settings. (Tip: You can also set how big the queue can get, I think some how, it's useful to set it to unlimited, but be wary of your memory usage and file sizes. :) ) -Dan. EDIT: Apparently Maya randomly decides to shut down the "Undo" script if memory gets to scarce or something, another quick fix is to go into the mel window, and type; flushUndo; and place that shortcut onto your Shelf.
BA Hons Computer Animation Arts is a 3 year degree course at the University for the Creative Arts, Rochester, UK.