Recently, I loaded up a saved flight and the a/c I was using, having previously been just fine, was just a black silhouette. On investigation, I found its texture folder was empty. Same thing happened with a couple of AI aircraft. Yesterday, same thing with the (flyable) a/c I was using and at the same time the sim flashed a lot of warnings about some object libraries I'd installed recently. I confess I didn't pay much attention to them and just closed them but when I went to look, I found that the texture and scenery folders of these libraries were empty as well (until now they were working just fine).
Does anyone know what might be causing this?