Hello!
Oops... yes! You can fix the save by editing "data" file inside the save file (it's a simple zip archive, so you can extract it, edit and compress back). You need to find "StartingCharacterTypeId" and change its value from "adventurer" to any other class ID: demolition, engineer, fighter, prospector, rogue, scout, trader.
I hope Lurler will explain why the adventurer class has been removed :-).
Regards!