Michael,
thank you very much for your quick reply.
I should have known I was doing something stupid. In fact, the registration didn't work because of a combination of mistakes.
First mistake was, as you suggested, that I was reusing the same ProgramID I used in Development for the Production systems. I didn't think it would matter, as those are for distinct systems: turns out it did. And I'm using a version of your doc where that warning is clearly stated at the beginning.
But that wasn't enough to fix the problem: turns out I also had made a mistake with the gw/reg_info and gw/sec_info parameters in ERP. The path didn't specify the file name extension, so SAP ERP wasn't reading those files, and was refusing the RFC registration.
Now I've fixed those two mistakes and the registration has worked. Thank you again!
Kind regards.
--
M