How many times have you made several changes in your model, then during regeneration -- well, at the failure of regeneration -- realized you changed something, just one thing, that caused the failure?
 

Next time you get to the resolve menu (the menu that appears when regeneration fails) instead of hitting UNDO CHANGES, pick FIX MODEL > RESTORE.  In this menu area you can examine the changes you specified, then select any that you would like to "UNDO".

This is also a good way to examine the changes you made, one by one, to see if perhaps you just made a typo, or perhaps put the decimal in the wrong place in a dimension.

Don't forget to pick REGENERATE from the FIX MODEL menu once you have made your selections.