Did you already update the SPL to the patched 1.09 version?
If so then usually you either missed to push the "0" button when the SPL asks you "do need an IU" or another application holds the USB - usually it is the Active Sync. Go to AS "Connection Settings" and deactivate USB connection.
To get the "IU query" you have to push the camera button when switching on and keep it pressed until that query comes.
To get better help you need to tell the exact steps you have done, so no guessing is needed.