Comment 3 for bug 583163

That fixed it

So rebuliding the library was what was needed (edit>collection>remove>apply and then edit>collection>remove>add)

I think this bug could be closed if the error message was a bit more explanatory. I initially messed around with mp3 plugins etc thinking that maybe the format of the file was wrong or something. I also tried reinstalling exaile. If it had said "file not found" (and ideally also suggested "the file may have been moved - please try rebuilding your collection") then I'd have recognized that my HDD manipulation was the cause and gone about fixing it without all the other experiments.

So please: a more informative error message than "resource not found" !