1.6.10 trying to burn boot loader with USBasp and I get a bunch of errors "Avrdude cannot find file..." Tried three PCs all the same five lines of errors each time.
It was only a few weeks back I converted all my Nano to Uno boot loaders with this same USBasp programmer so wondered if I was using 1.6.9 back then. Went back to that and all good. Must be a "feature" of 1.6.10. :)
Just saying in case anyone else has the problem.