IOS authentication with MS IAS (AAA/radius)

here is my config so far: aaa new-model aaa authentication login default group radius local aaa authentication enable default group radius ... radius-server host 192.168.2.12 auth-port 1645 acct-port 1646 key 7 ******

IOS (tm) 3600 Software (C3620-I-M), Version 12.2(29), RELEASE SOFTWARE (fc3)

i am able to telnet to the router ok, and authenticate via radius using my windows domain information, but when i attempt to 'enable', i get an error. on the IAS server, in the logs, it says $enab15$ was denied access... I understand this, but what i dont understand is why isn't it using my windows username when i attempt to 'enable'. or is there a way to force it to?

any hints/help?

User Access Verification

Username: username Password: *******

Router>en Password: % Error in authentication.

Router>

TIA