Hi Ady
I have seen this type of issue before and it was caused by incorrect setting of the reg_info and sec_info files. Please read the following note for more details.
1757655 - RFC failure - Cannot register TREX/BIA Registered
Server Program with Gateway
This note suggests apply the recommendations outlined in the following gateway note
1408081- Use basic settings for reg_info and sec_info.
Please apply this note and see if the RFC connection works afterwards
Kind regards
Barry