Hi Matt,
Can you clarify if you are using an IAS (2003) or NPS (2008/2012) RADIUS server and IAS Event Viewer possibly? If the RADIUS server is NPS it does not support MD5 by default, so the phone, if configured for MD5, would likely need to be changed to another EAP method such as PEAP for example, or use a RADIUS server that is setup for MD5. Microsoft no longer supports MD5 by default beginning with Server 2008/NPS. If this option is missing in IAS (2003) can you tell if is it available to be added in the matching RADIUS Policy?
Regards,
Scott Keene
Enterasys / Extreme Networks GTAC