Hi HomerJ,
I have seen this before in other clients where the issue was related to the user having special characters in their password and when authenticating against the system it wouldn't recognize the special characters. I have found the following documentation from HP regarding this:

Title : LDAP users imported to Quality Center and using a password with specific special characters are not able to login
Document ID : KM755834

Summary : Those special characters have their ASCII number higher then 127. The users should use a password without any special characters not within the ASCII (all characters of the password must be lower then 127).
Some of the LDAP users are not able to login to QC when others are able to do so. Those particular LDAP users who are not able to login are using one or several special characters in their password which has the particularity to have an ASCII number higher then 127.
Solution
The LDAP users imported to QC need to change their password and use only special character from the ASCII table (lower then 127).

I hope this helps you. In my clients case, removing the special characters in the password allowed authentication into the system, They then found a combination that allowed authentication and met their special characters password restrictions as the client was using a different regional setting on his local system than the server version was using.

Dan