It’s possible Michael_T can play with some shadows turned on. He’ll have to experiment to find out.
I’m not fully up on how openGL works, but it looks like they are using it to run the games rendering engine. The error is with a frame buffer object whose name is GL_FRAMEBUFFER_COMPLETE_EXT in openGL. Basically a chunk of data in a certain format used by graphics cards. You’ll notice a referral to that in the error message.
Graphics card differ a lot in how much data they can handle at once. There is always a limit to how many frame buffer objects any given graphics card can support. When a game tries to use more objects than the card supports, bad things happen.
Having said all that, I couldn’t even guess why it is only a problem when saving.
Edit: Actually, the game takes a screenshot of the game when saving. Which means some extra graphics grunt. That is probably why.