(going purely on memory, which in my case is spotty at best)
I "think" I may have gotten on of those errors while saving it that said something about 2 different version.. Sounding like I created it in one version, opened it in a different version and tried to save it in the newer version.
Like this one, but with different version numbers.
Also I think I clicked "do not show again" And way I can get that to start showing again for testing purposes?