Deus Ex: HR Saves Corrupted?

Hello, today I'm facing an error I've never encountered in any Steam game, whenever I try to save Deus Ex HR, I get the error "The game could not be saved". Even auto-save gives the same error.

Later I thought maybe the save file got corrupted somehow, so I saved in a new slot and that worked, however, when I re-launched the game, the new slot I just saved at was gone and my old slot had returned, kind of a rollback if you may.

Any ideas how I can fix this? Because I can't get any further in the game anymore :/