Found an "unposted resolution" from MS:
To resolve this behavior, first attempt to use the resolutions that are suggested in the articles referred to in the "Cause" section of this article. If you are still unable to resolve the behavior, or if the articles to not apply to your particular situation, follow these steps:
Go to the C:\Exchsrvr\Webdata\USA folder.
Open the Root.asp file, and then edit it:
Look for the line that reads:
if cint(days) < 0 then days = 10000
Change the line to:
if cint(days) < 1 then days = 10000
Save, and then close the file.
By changing this value to 1, you are prompted to change your password starting on the 15th day (which is the default) until there is only one day left. When there are no days left, you are then forced to change your password.
mojo