If you're having issues when saving the game, there are a few things we'd suggest trying to see if you can get this process to work successfully.
First of all, if within a save game try going to FM -> 'Save As'. When prompted to save, try saving to a different location than default (such as the desktop) and see if the game saves. If you can save there, then there is a problem with where your default Sports Interactive files are pointed and we'd suggest reading our FAQ on How to Change the Folder Location.
Sometimes anti-virus setups can interfere with Steam and/or FM, so it's also worth reading and following the instructions here - How to make sure that an Anti-Virus Program isn't interfering with Steam or FM?
If you're having an issue where the game seems to be saving, but you can't see if within FM (only within the folder location) please read and follow the instructions here - How to change the Sports Interactive folder location
As a final warning, we would very much suggest NOT using any custom unofficial apps with the game, as these have not been tested and cannot be guaranteed to work. Any unofficial scouting or editing apps have the potential to cause severe problems.
If nothing above works, please create a Support Ticket stating exactly what you've tried so far and a member of our team will try to help.