I have not seen this before, but I would suggest to check the settings of your registered LDAP servers. Please use the hostname or domain name (DNS style name). Make sure, that you test the connection from the wizzard page.
Yes I have exactly the same problem on a 64bit install of ePO4.6 patch 1. 32bit is working fine.
LDAP setting identical for both & wizard reports sucessful connection when testing
If the user's password is changed then please write the new password under group mapping=>AD credentials.