751e44c4__Error_Codes___ServiceNow_Wiki__Description
[Error / Data Code] 53 [Error] LDAP_UNWILLING_TO_PERFORM [Description] 
Indicates that the LDAP server cannot process the request because of server-defined restrictions. This error is returned for the following reasons: The add entry request violates the server's structure rules...OR...The modify attribute request specifies attributes that users cannot modify...OR...Password restrictions prevent the action...OR...Connection restrictions prevent the action.
LDAP Error Codes - ServiceNow Wiki
Description