As BATTLETECH doesn't officially support mods you should be aware that using mods can cause unexpected problems that we aren't necessarily able to solve, however, we do have a workaround that should fix it.
- Reinstall the mod(s) associated with your saved data
- Load game, custom mechs, custom lances; or whatever it is that's not working
- Strip and destroy all mechs/components/lances etc. that reference data from the mod
- Uninstall mod
- Game will run normally