This usually means the save file was corrupted. Restore your backup.
The file is usually named save_file.dat or similar. You can find it here: C:\Program Files (x86)\Steam\userdata\[YourUserID]\204360\remote\ 2. Backup Your Data castle crashers save editor steam
Editing your save can sometimes trigger achievements instantly. If you prefer earning them "legally," be careful which boxes you check. Common Troubleshooting This usually means the save file was corrupted