Mountain Lion Bluetooth SPP resource busy/no pty

I've paired a data collection device to my MacBook Air via Bluetooth. I looked in System Preferences -> Bluetooth and see it listed. The detailed view confirms that SPP is an available service. I check in /dev/ and I see:

ls -l *Gb*

crw-rw-rw- 1 root wheel 33, 5 3 Oct 22:59 cu.Gband-7-SPP

crw-rw-rw- 1 root wheel 33, 4 3 Oct 22:59 tty.Gband-7-SPP

(The device's name is Gband-7).

When I try "sudo screen /dev/tty.GBand-7-SPP 230400" in a terminal on my MacBook Air I get a "cannot open /dev/tty.GBand-7-SPP for R/W. Resource busy.", followed by "Sorry, could not find a PTY".

I tried:

sudo lsof | grep "*Gband*"

which returns nothing, so it does not appear that the tty is in use. Rebooting does nothing useful. I cannot find any obvious permissions problems.

Any ideas?

PS: Everything works as it should on my 2008 MacPro, also running ML 10.8.5.