Hi Pradeep,
I was fighting with the same problem (error message) at a customer some time ago and we finally re-established the trusted connection via SMT1, because even with full authorizations for S_RFCACL it did not work. It seemed like the trusted relationship was broke, but we were not able to find out the root cause for it. Due to the fact that this happened in a QAS system, it might had something to do with system refresh actions after copying PRD to QAS systems - but I am not sure if that is really a reasonable explanation.
For using trusted RFC connections a normal enduser only needs authorizations for object S_RFCACL as well as authorizations for accessing the called function module via object S_RFC. Objects S_RFC_ADM and S_RFC_TT are not needed by endusers, these objects control whether you are authorized to manage RFC destinations and trusted connections.
Best regards,
Stefan