I think Deane is probably on the right track. The other possibility is the two-way function settings. If you have any of these set to two-way they could be sending out status request that would be preventing other commands from getting through, this would especially be the case if one was set for two way and the other was not. You should be able to see this activity on the PCS led though. The PCS led will blink red when it sees activity and green when it recognizes it is being talked too.

Bill
www.homeautomationnet.com