I too have this UNDOCMD error on one of our projects. Seems to be an isolated issue, as I've not had this problem with other dwg's. But this particular problem child is a set of three dwg's that were once one big dwg. For necessity, they had to be broken up (it had ballooned to 70 MBs and there are a lot of xrefs and data refs). But, in the meantime I've had countless Fatal Errors and crashes. So I think the dwg's database has some corruption. Running Drawing Recovery, audits, and regapp didn't fix the problem. Repairing and reinstalling didn't fix the problem either. (even after a clean install)
Someone here suggested trying True View (http://usa.autodesk.com/adsk/servlet/pc/index?id=6703438&siteID=123112) and I gave that a shot. I used True View to convert my corrupted dwg's from 2010 down to 2007. Our problem with the UNDOCMD 2 error is when trying to save the file. (crashes) But, it doesn't crash if I save the drawing down to 2007. So, I used True View to convert down to 2007 then opened up the dwg and saved it (2010 format) and that seems to have worked. I was able to open the dwg again and save/close the dwg without crashing.
I'll know over time while working with these three problem dwgs if this remedy works for sure. But give it a try it to see if it helps your situtaiton.
* Note--I don't have any issues with these problem files if I open them in another CAD ver., ie, 2012 (on a different PC).
The TrueView remedy did not work. It worked for about one session, but after opening the dwg back up, the dwg crashed on an autosave. This is only happening to these particular drawings as I am not experiencing this error on any other drawings (large or small).
So, I am still in search for a cure. (audits/drawing recoveries report zero errors) The only other option I think is to simply create a new drawing and copy & paste, etc.