Could you :
- Call RFC_READ_TABLE with only the required fields, so check if problem came from table width,
- Ask also basis (or check yourself) for some authorization check (hidden by the system due to security notes) using same user id than in the RFC call, try VIEW_AUTHORITY_CHECK or check authorization objects as S_TABU_NAM, S_TABU_DIS, S_TABU_CLI, or S_TABU_LIN.
Hint: In recent systems basis guy may be able to audit the call of generic table access tools in target system - 2041892 - Logging of call of generic table accesses
Regards,
Raymond