start /DC:\Program_Files_(x86)\Bitcoin\poclbm poclbm.exe --host=deepbit.net --port=8332 --user=REMOVED --pass=REMOVED
it thinks that --host=deepbit.net is the software that it should run!
just remove the last "\"

Also, use pit.deepbit.net rather than deepbit.net as your host.
You probably want this assuming your are running a 58xx, 59xx, 68xx or 69xx series Radeon card.
start /DC:\Program_Files_(x86)\Bitcoin\poclbm\poclbm.exe --host=pit.deepbit.net --port=8332 --user=REMOVED --pass=REMOVED -v -w 128 -f 10
Remove the -v and -w 128 if you are using NVidia hardware. Also, you can adjust the -f 10 value lower for better performance (many people run -f 1) at the expense of desktop lag and higher to regain some of that lag. It can also affect stability if set to low. If you are running Windows Vista or Windows 7 and the machine is dedicated for mining, or you don't care, turn off Aero.