In sm59 you are trying to create HTTP Connection to ABAP System
Following entries are added
1 Connection Type: H
2 Target Host: Host name
3 Service Number: HTTP Port name
4 Path Prefix: /sap/XI/engine/?type=entry
When You try save RFC, message “Query string not allowed” occured.
After you enter the Path prefix /sap/xi/engine/?type=entry, press Enter saved the entries ..