This solution has been verified to work on Droid 2 and Droid X models running Android OS 2.2 (FroYo). 

Froyo 2.2 users might receive multiple requests for Pin code set-up for their Exchange account. This can occur even if not requested on server side. To remove this requirement from the handset you can try this workaround:

1. Remove corporate exchange account.
2. After removing account, the phone will allow the removing of the pin. Go into Location & security > Change Screen lock in your settings menu and turn off the Pin/Passcode lock (set to none).
3. Once the pin is removed, re-add corporate exchange account.
4. The phone does not request pin again

Information was taken from Motorolas knowledge base article linked here.