Hi Che,
Please check the below discussion and check the reply of Mark
Proxy problem. INTERFACE_SIGNATURE_ERROR ??
The error you get: INTERFACE_SIGNATURE_ERROR means that the proxy object has got inconsistent against his definition in the ESR. You can check this in trx SPROXY -> open the corresponding object,
and choose 'check proxy' from the context menu (or Ctrl + F2)
regards,
Harish