inn2, innfeed.log : 501 Unknown MODE variant

Hi,
I set up a slave server.
I'm sure I've got a configuration problem.
Innfeed.status (slave server)
   want streaming: yes      active cxns: 1
   is streaming: no     sleeping cxns: 0
Innfeed.log (slave server)
- Adding peer: NUO
- NUO:0 Issuing the streaming command
- NUO:0 Processing mode response: 501 Unknown MODE variant
- NUO All out of articles in the backlog
- Host is idle: NUO
(NUO is the production server)
An idea of what causes the: “501 Unknown MODE variant”
and prevents the streaming mode ?