I have seen "MinNumberOfUndos=10" :)
What that? (I have made 24 undo without problem :)

An error script (It's my fault :)
I make a box 3 D (By corners) but clic the second corner on the "same line" ! (yes it's a shame :)
--> Error script "Line 126 Column 0"
That don't block the prog :)
I close the message, the 2 points are automaticaly deleted and I can continue :)
Maybe a message like "you have made a mistake" will be appropriate :)