I know there is no On/Off button for this -- it may be the Undo/Redo buffer gets "full", or otherwise stops functioning. Or, it might be that something that you were expecting to work, is not an operation that can be undone?
If you post the specific things that fail to work, or when they don't work, along with a few details about DataCAD and your system, then maybe folks can get closer to a solution for this.
I have had this happen - but rarely. I think that Neil's guess may be correct. I've never been able to track down the cause; I sometimes think that it might be a confusuion caused by multiple applications running at the same time and windows and DataCAD get mixed up about which application is controlling the undo buffer - but that's just a surmize. If I close out of DataCAD and restart, the function works correctly - the problem doesn't seem to "carry over" in the drawing file.
I have this same problem and it often occurs several times a day, but in my case all the keyboard shortcuts cease to function. In fact, if I use the pull-down menus, the associated keyboard shortcuts that are usually shown do not appear at all. If I have multiple drawings open, all I need to do to make the keyboard commands re-appear is to switch to another drawing where they show up, then switch back to the drawing that was trouble and, voila, they're back.
Seems like a bug to me because I cannot find a pattern or cause and it's been a problem for me in all iterations of v11. At least I can easily work around it, but I'd rather not have to.
