WHMCS has acknowledged that this is an issue with their update. However it sounds like they will not be making any changes with it until their next update. The password can be changed directly in the MySQL database. Here is what they gave me. It includes the SQL syntax to change the password.
****** From WHMCS ******
Apologies for the delay in response. Since my last reply, there have been other reports of this error and we are aware that this is a regression in the 5.2.14 release. Case #3727 has been opened with our developers in order to have this resolved for future releases. Unfortunately, I cannot provide an estimated time for completion for this. However, once we resolve cases and push features they are available at our change log, here:
http://changelog.whmcs.com/
I apologize for the inconvenience, and appreciate your patience as we work to resolve this. In the meantime, you can still manually reset an admin password in the database using the following SQL query:
UPDATE tbladmins SET password=MD5('<password>') WHERE username='<admin>';
In the above, replace <password> with the desired password and <admin> with the correct admin user name.
If you notice any bugs in future, please use our new bug reporting tool at http://bugs.whmcs.com
