VMWare ESXi monitoring not working

I have some problems with monitoring the VMWare ESXi servers. I did the following things:

VMWare Esxi
- Enabled SSH
- Enabled SNMP + String + Agent started

OPManager
- Imported the ESXi machine.
- Tested SNMP credentials (working ok!)
- Tested Login credentials SSH (not working!)
- Tested some SNMP monitoring (example: CPU Utilization, not working!)

So finally the SMNP string communication is working but that's it .... I don't see the virtuals etc. Can someone help me with this. I've checked the Forum but didn't find any solution.

We are using:

VMWare Esxi 3.5 (build 103682)
OPManager (latest trail version with ESX monitoring support).

Thanks!