The USB Autoscore drivers are probably the exact same drivers you can download off the support section of Mylaps. If you have the decoder showing up in the devices list, you should be good to go.
That's a strange error message. If you don't have a printer installed (installed, not necessarily connected), you should get an error message along the lines "Autoscore requires a printer to run", but if you click OK, it continues.
Autoscore is unfortunately very picky and buggy. Sometimes it installs perfectly and other times you get frm errors that fatal. I remember diagnosing a bug with Bill (the developer). It had something to do with an update he wrote and it not being compatible with the ini file the program used from the previous version I had installed. It took lots of trial and error to figure out it was the .ini file, but eventually Bill wrote a patch to fixs that bug.