Hi There,
Firstly I would suggest you download the latest SWP for the UC-520.
Secondly extract the SWP and in there you will see various default configuration files, make sure you choose the right one for your UC-520 this is quite critical that you do.
Thirdly, if you are having troubles communicating to it, then I would suggest you manually copy over the default file (It is a .cfg file) to the Compact Flash Card by using a card reader and and copying it that way (I always had one in my bag with me, you just never new when you would have to resort to this method).
Get your system back to factory def