I don't know why. All me already-downloaded songs work, but every time I download a new one and try to open it, it brings up a message that says "Unknown File. Loading Aborted" ...
when does it give you the message, during the download or when its done and you try to open it?
when its done and I try to open up. Guitar Pro opens up, its just a blank tab with the message.
try downloading them from somewhere other than UG maybe?