Thank you very much Ananda Divine. I wasnt sure it was an engine version thing although I had a hunch, cause it had worked for me before aswell.
The only thing I can give you (cause I still havent found the answer), is an alternative, which is to just reimport from scratch the animations in .fbx format and then attaching them to your new skeleton. You probably new about this rudimentary solution though, and it surely doesnt solve out problem.
Best regards!