Reset Customer Password

Had a customer who had purchased an item and registered with a password. He then attempted to check on his order a couple of days later and was told his email or password was invalid. He clicked on forgot password but never received a new one. Did this a couple of times.

I went into his account and the email address is correct. I then attempted to reset his password via the image below but got the error message at the top of the image. Am I able to reset the password on his account? If so, what am I doing wrong.

Thanks