When you use the Add Bluetooth Device Wizard in Windows XP SP2, and select Let me choose my own passkey, you receive:
We recommend using a passkey that is 8 to 16 digits long.
If you press the Back button, the message should instantly disappear, but it persists for five or more seconds.
I guess Microsoft wants you to remember to use a passkey that is 8 to 16 digits long.
This behavior does NOT affect the functionality of the Add Bluetooth Device Wizard and can safely be ignored.