Hi Chintu
If you tried posting a GR document and it did not get posted I assume since there was an error message in the portal you would not see an IDOC generated for it ... hence you do not find one in the backend ..
If the GR successfully got posted from SRM and did not reach ECC then try searching for outbound IDOCs from SRM and there you will see the GR document ..and if its stuck in error ..
To be able to post the GR correctly the error must be rectified .Take help from FI team member or MM ..
Also you can try posting in ECC directly and it should give you the same error since the errors generally come from the backend
Hope this helps ..
Regards
Vinita