I basically had a bunch of mods installed and then when I changed computers and installed Inquisition I just couldn't load in with my previous, current playthrough. Then I re-installed everything that came with the game (like DLCs, and such), still gave me the same message, so with DAIMod, iirc, I merged all the mods I had installed again, still gave me the same message. I opened the initial menu again and decided to connect it to the Dragon Age Keep I(never usually did this before) and after that I loaded the save without any problems.
Hope this helps you : ) Also sorry if this reads weird and has spelling mistakes, English isn't even my second lenguaje.