Originally posted by Captain Spaulding:

Hey all Ive been playing co-op with a friend and I was in the middle of working on a small vessel thats incomplete. This morning I loaded up and my small vessel is nowhere to be found and now i get that internal error message popping up when Iog on. Any ideas what the solution is? Thanks

Unfortunately there's probably nothing you can do to recover the ship. This is why it's important to frequently save the blueprint of a ship you're working on designing.
You could report this on GitHub and I'll mark it as a game bug there in case anyone else has the same issue they can find it, but there's nothing I know of to recover it in a single player or coop game except for one method that might work.

If you want to try that method, please open a GitHub issue and I'll explain it on there but it involves copying files and such and probably won't work in your case anyway.