"Unhandled Exception: Microsoft.EnterpriseManagement.Common.DiscoveryDataInvalidRelationshipTargetException: Invalid relationship target specified in the discovery data item"
The Syntax to approve the gateway is:
If the RMS is clustered you should use the cluster virtual name rather than a physical node name to approve the gateway. If you use the physical node name you can get this error.
Note: In the above scenario the approval tool is running against the Clustered RMS as the Gateway will report to it. If you want your Gateway to report to the Management Server then use the stand alone Management server name.
Hope this helps,
Satish Phatge | Operations Manager Support Engineer