Ucs slave cannot login

I upgrade my domain master to 4.4.8 from 4.4.3
and my slave version is 4.4.3
when i loggin to my slave :
Internal server error: The service is temporarily not available.

Cannot connect to the LDAP service.
The following steps can help to solve this problem:

  • Make sure the domain controller master is running and reachable from ucs-slave.ucs.com
  • Check if enough hard disk space and free RAM is available on this server and on the domain controller master or free some resources
  • Restart the LDAP service on the domain controller master either via “service slapd restart” on command line or with the UMC module “System services”
  • Install the latest software updates

How to upgrade my slave? thankyou