After spending a few frustrating hours on why my SAP RFC call was not returning data and the call was successful . We founf this little gem here from the LOB adapter team blog
If you're sending messages using the channel model instead of using a .NET proxy (for example, in BizTalk) - if the table node is missing from the input XML, we interpret that as if you're not interested in that table. If you do want the rows from that table in the response message, you should pass in the node in the input XML (0 rows, just the starting and ending parameter tag).
