Allamudi,
I don't think so.
In XI's Configuration Guide I can see some text: Http error 500 is normal state of communication/
.
Yes, it's so strange and many people ask about it in SCN.SAP.
Anyway I see the same situation with the connection test - in PI and ERP side, thought in PI side it was generated automatically.
PIISUSER (in PI) is ok and he has SAP_ALL permissions.