Could be you need a smaller relay, any idea what the BOB's rated output current is?
Try some other loads on it like an LED/resistor, filament bulb, etc and see if it fires them up ok. also, does the relay work with a plain 5v supply to it?
I used some darlington pair optoisolators on my machine, these provide 5kv isolation and will drive a small relay very well. Worth considering. A phone charger makes a lovely packaged 5v supply.
Edit: is it one of these?
http://www.mdfly.com/index.php?main_page=product_info&products_id=87If so you will have only the power available from the parallel board to drive your relay, and it probably won't be enough. most parallel boards only really supply logic level currents.
http://campbelldesigns.net/Combo-board.php - This sort of thing may be more to the point since it is designed to drive relays. Plenty of options avalable, and most of them feature optoisolators which will stop your computer going to glory in the case of your wiring having a fry-up.