Hi Dilip,
SAP PI being a hub system shall ideally have the highest release in entire SAP landscape in comparison to other SAP systems integrated via PI. This is a common guiding principle - refer to a SAP Note 1043047 and Notes mentioned in it for more details about reasons for that. So it is absolutely fine to run SAP application systems of lower releases and integrate them via PI system of a newer release.
Regarding the error in RZ70. If you provide more details on it here, it would be easier to make further analysis.
Regards,
Vadim