I sometimes connect my Mac to the Internet through my mobile phone’s 3G data connection. My Mac talks to my mobile phone through Bluetooth, and my mobile phone functions as a Bluetooth modem.
It generally works great. But, from time to time, the Bluetooth modem just stops working. The errors repoted in /var/log/system.log would be something like:
Modem error; the modem is not responding. CCLExit: -6019 (Modem error, modem not resopnding.) Connect script failed.
Failed to open /dev/cu.Bluetooth-Modem: Resource busy
Often, the modem never works again, and the only solution is to unpair my mobile phone, and go through the Bluetooth pairing and setup process all over again.
Now, I think what works for me seems to be this: Disable the wireless LAN (and disconnect any wired LAN cable) first, before attempting to connect to the Bluetooth modem.