Security areas are requiring end-users to use passphrases now for passwords. It consists of 3 or more words with spaces in between. LDAP authentication works well for 3 words with spaces in between. However, authentication does not work if the password has space at the end (trailing space).
Clarity PPM 15.8.1
When Clarity PPM is configured to use external authentication, the authentication is handed off to Active Directory, in your case. CA PPM will not be involved in the authentication. The user's password field is grayed out in Clarity PPM when external authentication is enabled. Your Active Directory server controls what is allowed or not allowed in passwords.