I inscribed on this forum because I had the problem to do not beeing able to syncronize anymore via bluetooth.
When I was pairing the PC I only found "Serial Port" as service instead of "ActiveSync".
In this forum there was an identical topic that suggested a procedure that works for sure, but it suggested an Hard reset that it's a bit too extreme!
I strongly believed that there was a less drastic solution, so I went on in searching on the net and I finally found it.
I'm not sure if this applies only to the cases similar to mine, where I ALREADY used the bluetooth sync.
The simple thing is to:
1) turn off the bluetooth on your PDA
2) in the PDA registry delete all the keys below HKLM\Software\Microsoft\Bluetooth\ActiveSync\, dont delete the key "ActiveSync" itself and the DWORD values "BatteryPrompt" and "Initialized", and the binary value "LastConnected". There should be one or more keys with a 12 hexadecimal characters name: delete them all.
3) Pair the devices again (maybe you will have to delete the old pairing in both sides)
Here a free PDA registry editor.

Ciao
marcotti