I had a similar problem with the 350 series. I receieved the following information that resolved my issues.
******
Using RADIUS, You need to use cisco AV-Pair attribute for admin users with following syntex
aironet:admin-capability=write+ident+admin+firmware
Here is the procedure for the admin user you to define the Cisco AV pair Attributes .
a) On acs select the interface configuration and go to the advance option ,
selct "per-user Tacacs/ radius attribute " click on submit .
b)On ACS , Select network configuration ,
1) check if you have configuration >> Radio ( IOS /PIX available ) on the ACS
if not add NAS type Radius IOS/PIX , note that this needed for IOS / PIX attribute
2) After adding IOS/PIX device , select interface configuration >>Radius ( IOS / PIX )
Enable [026/009/001] "cisco av-pair" option , again make sure that you enable
at user and group level click on submit
3) Add a user ( User setup >> ADD/EDIT ) to restrict administrator access control
1) enable and configure cisco 09\001 cisco av-pair using
aironet:admin-capability=write+ident+admin+firmware
http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo_350/accsspts/ap350scg/ap350ch8.htm#1073082