An error message like
"could not open session" is often the result from error in the authentication proces. In Linux is that the PAM stack, pluggable authentication Modules.
By default most distro's log authentication error messages in
/var/log/secure. Start by checking there.
As discussed in chat: in this case the error originated from the
pam_mkhomedir module that creates home directories for users when they log in for the first time and no home directory exists yet.
The base directory where the home directory is created must exist, in your case
/Users/ but that single user that generates the error was incorrectly provisioned in the LDAP directory, with a home directory in
/User/ missing the the plural
s. Since that directory did not exist pam_mkhomedir failed and access was denied.
Solution: best is to correct the homeDirectory account property for that user in LDAP.
Work-around: simply create