I am trying to register the ZLMAgent 7.2 from a SLES10SP1 to my ZLM 7.2

The installation goes ok and everything looks fine but when I try to register the system with my ZLM using rug :

rug sa -k registration_key https://ZLM_Server_address

I get and error :

ERROR: Could not add 'https://ZLM_Server_address': Download failed: (https://ZLM_Server_address/zenworks-...on/service.xml) Error getting response stream (The remote server returned a 502 status code.):SecureChannelFailure

I have tried with different systems and I get always the same error

Any advice?