Hello all

I'm having a problem where I have an assembly that has a part with two configurations in it, I opened the assembly today to work on it, this message popped up (http://puu.sh/1S2u2) and it was in its default configuration (not the one I wanted for the assembly) and when I tried to change it to the second configuration, it wasn't there. I opened the part and the configuration was just gone, this isn't the first time something like this has happened, does anyone know why this happens or what causes configurations to just dissappear? Is it safer to just make complete seperate parts? Is there anyway to recover the configuration?