Well I opened a new project and it is working now, so I assume it is a bug in the project file.

I am using Reason 12.7.4d3 (build 15815) (stable channel).
Not sure what to do but I can nt use the undo function.
If I use either ctrl+Z or the undo from the drop down list, it does not work.
What am I to do? Any experts got a clue?