Device not monitored

Hi all,
I have just recently installed OpManager 11 (previosuly I had a working OpManager v9, but I did a complete new install without migration).

I want to monitor a remote AIX computer over which I have little control.

I can use SSH to connect the that server, so I configured OpManager to use CLI monitoring.

As soon as I start OpManager, it seems to correctly fetch the values for disk utilization, memory utilization and cpu utilization, but shortly after I get a red warning in the summary page of the server:

"Device Not Monitored.
This device is presently not reachable. OpManager will detect and rediscover the device once it is up."

And then I get no more values for CPU, Disk and memory.

I tried several times to re-enter credentials, without success (the "test credentials" button always reports failure).
Note that I can connect to the AIX server via PuTTY from the same PC where OpManager runs.

Any hint?

Thank you in advance
Cris