importing RFC from R/3 3.1i PI 7.0

Hi,

The scenario is picking a file from third party FTP sever and posting an Idoc into SAP R/3 3.1i using PI 7.0. In between we call an RFC from R/3 3.1i from PI 7.0 for converting values. The problem here is, where we tried to import RFC from R/3 3.1i into PI 7.0, its is not allowing to import.It says unauthorized access, even though i had permissions to do that.

1:) Is this a compatible issue?

2:) Can we import RFC from 3.1i into Pi 7.0? Then why i am not able to?

3:) Is there any other way to use that function module in mapping?