This is really strange:
The password that the user account was changing to did meet all of the necessary requirements.
The user was trying to change the password as it was the one we gave them when we needed to reset it.
After a little digging around, this is what we came up with:
The minimum password age is set to 2 days in the SBS 2008 Default Domain Policy.
So, the user was instructed to keep using the current password and change it early next week.
As an aside, we always instruct our users to never change their passwords on a Friday. There is almost always a phone call to us on Monday asking for a password reset!
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book