I've been entering my family tree into MacFamilyTree however, if I export and then attempt to import the GED file into Ancestry, it reports as an error and I don't know what?

I had the same problem so then I thought maybe it was my software. I deleted it & went to reinstall it but I lost my mom's serial number (shes deceased) & now have to pay another 50. :(
I contacted them about it and they couldn't figure out the problem. (nor would they issue me another key). I wish you luck. Keep us informed if you found the problem.