Windows Server 2008 R2 adding as node issue

Usually you can isolate it by looking whether :

1) communication lines are open, and

2) appropriate permissions have been granted.

It sounds like you're already done with # 2.

Can you check # 1?

You may want to install and launch a packet capture from the SolarWinds server itself.

Filter the packet capture to display and save only those network traffic that either came from or got sent out to the IP address of the Windows Server 2008 R2 machine in question. See if (1) the SolarWinds server is sending out WMI connection requests to the target machine, and (2) if the SolarWinds server is getting any replies coming from that Windows server.

Hope this helps.

I would agree with ekis.....when I have run into that issue in the past, it's generally been connectivity...local firewall or some vlan that the poller didn't have access to.