Error in MOC file

[schnitzel]

have you tried doing a project clean?

sometimes Qt Creator can get a bit confused when the designer generated code gets out of sync, I usually do this:
close Qt Creator
delete debug/release folder
delete Makefile.* (there should be three)
delete object_script.<proj name>.* (there are two of these)
delete <proj name>.pro.user

reopen the project and rebuild

make a habit of archiving your project before tinkering with things in the designer.

I just realized that you actually solved your problem - oh well, the above steps are still useful for doing a project clean manually.