Hello,
Remove the IP affinity to the protocol, SNMP. I've just delt with this exact issue. Removing existing affinity to snmp worked upon next Discovery. SSH is credential is valid on the box, will be tried first over SNMP, assuming the priority order for protocols is SSH before SNMP (which is the default order I think .. )
In my case, the Linux box had 2 protocols and Discovery had a preexisting affinity to snmp.... Hence disco was not trying SSH...
Hope this helps?
Dave
