Write community string is unnecessary. You can remove that from both the SNMP service configuration, as well as while adding the node
For the SNMP service, what do you have in the access list section below that? Is it set to 'Accept SNMP packets from any host' or 'Accept SNMP packets from these hosts' ?
Tried restarting the SNMP Service already?
Copy the snmpwalk.exe utility from the NPM installation folder to the 2008 R2 server, and try to do an SNMP walk locally. If it is responding locally, something else is blocking the queries from the NPM server