Another 2 cents--
I have just encountered this problem, with AutoCAD 2011. I couldn't save a drawing, plot it, or use plot preview from the quick access menu bar. I attributed the problem to 3D commands--mesh editing, etc.--but had no real reason to do so. Although I couldn't save or plot, I could execute other commands. Following an earlier reply, I entered Save at the command line, successfully saved the drawing under another name, opened that drawing, which I could then plot.
Here we were facing the same problem and one of the guys that work here and he came with the following solution:
When starts the AutoCad open a file and on the comand line type "filedia" and then type the value "1". That totally solved our problems.