Got that a lot on my Tungsten T with D-Link DBT-120 adapter. It's been discussed on a few forums - Palm tech support, Treocentral, with no definitive fix.

Try deleting the Bluetooth serial port and deleting com.palm preferences as described above. Soft reset the Palm and restart your computer. Then recreate the serial port and set up HotSync Manager (also as above). Give it another go and see what you get.

Usually what fixes it for me is to just keep trying over and over, eventually something will come out differently and it'll work. Wish I could be of more help...

I had the same problem with my T5 after trying the described hint; I skipped the part with disabling HotSync and the Prefs. So, After disabling HotSync, deleting the com.Palm - Prefs in that Preferences/ByHost - folder and enabling the BT-Port again (I didn`t delete it, it automatically got unchecked in HotSync Manager), all goes well here.