Invalid signature in 'change password' field

I have the following error on my Domino R6.5.1 server in the AdminP database, all errors by date section, under the change user password in Domino Directory process:

The signature in the Change Password field was found to be invalid

Any help will be greatly appreciated.
I haven't run into that one before, but my guess is the directory was originally signed by an ID that is either expired or recertified. First, I would suggest signing the database with an ID that has full administrator rights to the servers in your domain. Make sure this ID has all of the authorities needed on your servers to process any agents that may run via the directory. If that does not fix the issue, I would open up the person document form, go to the "Change Password" field, enter a value, erase it and save. This will effectively change the signature of that field. Finally, you could/should also resign the Administration Requests database with the ID. Again, make sure the ID has all needed rights on all domain servers to allow the agents to properly run.

Member feedback:
Thank you for the prompt response, and thank you for answering my question. Your response makes sense, and we will be able to solve our problem. I cannot find the "Change Password" field in the directory. What field are you referring to?

Mike's response:
I wasn't looking at a directory when I wrote this, and "Check Password" sounded correct. I believe the field you are looking to fix is the PasswordDigest field in the Person document.