SIM 6.3 - when adding ESX 4.1 server showing system type "unknown"

[MonitoringatSky]

I am successfully managing a lot of ESX servers (2, 3 + 4.0) from SIM 6.3, but have recently added a number of ESX 4.1 servers. None of them are discovering properly.

Getting this during discovery (just the relevant parts):

        * Checking for SNMP protocol support on system...

Normal:   The system responded to an SNMP request; it supports SNMP Protocol

          and has a valid read community string.

        * Running SNMP System Type manager ...

Normal:   No matching SNMP System Type Manager rule for sysObjID was found.

Critical: There are no valid WBEM / WMI credentials for the system(s).

        * Running WBEM rules based identification...

Minor:    Identification cannot get computer system hardware data from the

          WBEM / WMI providers.

        * Running Virtual Machine (VM) Host (non HP Integrity VM Host)

          Identification...

So SNMP look OK, but WBEM doesn't.  

I don't build the ESX servers - I just ensure they are monitored, so troubleshooting is painful.

Any advice appreciated.