- Which version of SNMP have you configured on your router? SNMP v3?
- Have you checked if there as any access list defined on this router that might limit SNMP queries from specific IPs only, and perhaps SolarWinds server IP is not in that list?
- There is an SNMPwalk.exe tool directly under the Solarwinds installation directory. You may want to try and do a MIB walk using that tool first. If it is SNMP v3, it is usually a matter of getting the correct authentication and privacy settings. This guide should definitely help http://www.solarwinds.com/documentation/Orion/docs/Implementing_SNMPv3r1.pdf
- Does the MIB walk tool show any OIDs at all in it's output? If the SolarWinds server is in a different network segment than the router, try copying just the SNMPwalk.exe to another Windows server on the same network segment and see if it responds from there. If it does, then something is blocking SNMP in between