751e44c4__Error_Codes___ServiceNow_Wiki__Description
[Error / Data Code] 12 [Error] LDAP_UNAVAILABLE_CRITICAL_EXTENSION [Description] 
Indicates that the LDAP server was unable to satisfy a request because one or more critical extensions were not available. Either the server does not support the control or the control is not appropriate for the operation type.
LDAP Error Codes - ServiceNow Wiki
Description