RogueSwordsman

I've came across a strange problem when attempting to return to a project I've been working on. Everytime I attempt to, I receive the following error message; 'Invalid id -4 in CppProject::Asset::Find:71' I'm not entirely sure what caused this problem, since this is the first time this has happened to me, and I'm afraid that I may lose my data. Is there any way to properly fix this?