I have installed a Belkin F1U109 Reversible Parallel Autoswitch (had it knocking around for ages), to use 2 printers with one PC. The software seemed to install OK and I've followed all the setting instructions but when I try to print a test page on either printer, I just get the beginings of the top of the page on the Brother HL2040, then the rest of the page is blank and it goes on churning out endless blank pages. The other printer (HP deskjet 940C) just prints 2 small diamonds in the top left corner, then does the same as the HL 2040.
Check your connections. I've found that when a printer connected to a parallel port starts churning out crap the cable is invariably at fault.
I assume that now you have one printer connected to a USB port you have dispensed with the switch. Ensure that the printer end of the parallel lead is sucurely fastened to the printer, and the PC end is fully screwed in.
If this doesn't solve the problem try using a different lead, as any break in the wire will cause problems, long wires often get chair wheels rolled over them which can damage the wires.