I've created a test account called radiustest in my 2003 based Active Directory and created a 2008 based Network Policy Server. Here is the service test I'm trying:
check_radius_ih -r $HOSTADDRESS$ -c 1812 -s secret -u radiustest -p ABCd123!
All attempts return:RETURN CODE: 2 (CRITICAL) OUTPUT: CRITICAL: Access DENIED. (code = 3) | rtt=0.0046 rttms=4.6429
I've logged in as that user to a workstation to confirm it is active.
For each attempt two errors are logged in the Security Event log on the NPS/RADIUS server. First a 4625 (0x6000006a and 6d), then a 6273 (reason code 16). Both are associated with an incorrect password
We have used several RADIUS test clients with this server and verified that it will authenticate correctly.