I get a ridiculous undo buffer error while attempting to make ANY edit to video projects.

This only recently began.

I have tried the save project under new filename, re-open the program and start again. That worked for awhile, but now, I cannot even make one edit and the message pops up.

How can there really be an undo buffer error when I have not made one change yet>

I am running a quad core processor
4gb of memory
2.83ghz
windows xp home sp3
on a 500gb hard drive with only 40gb used.

Any ideas for fixing this?