I am currently experiencing Windows 2003 servers whose interfaces become "Unknown"
I found the following articles:
http://thwack.solarwinds.com/thread/28814
and
http://thwack.solarwinds.com/message/87011#87011
They reference a Microsoft article: http://support.microsoft.com/kb/972840/en-us
However the issue I am experiencing is with 32bit systems and the hotfix is for 64bit systems.
My current workaround is the restart the SNMP Service on the node that is experiencing the issue, but it happens at least once within a week and the more nodes we are the more its a pain.
I"m currently running the following:
Orion Core 2012.1.0, SAM 5.0.1, IPAM 3.0, NPM 10.3, NTA 3.9.0, IVIM 1.3.0