Well, i prubed different IOS version to solve the busy problem that i reported in the list last week, by the way, thanks to all for your comments and help. Finally 12.0.5(T) appear to be good, but i'm not sure yet.

Now i find a problem with the authentication over the radius server ( a windows 2000 advanced server running IAS), with certains modems, specially USR 56K external, the as5200 fail, if i see the logs in the radius i see something like this:

User WmeTeO=erST        c*YXf,4v!X+(A)[3{m^C}ear^*hLEm/a/FdP'mV?+ was denied access.
 Fully-Qualified-User-Name = RADIUSDOM\WmeTeO=erST      c*YXf,4v!X+(A)[3{m^C}ear^*hLEm/a/FdP'mV?+
 NAS-IP-Address = 172.17.101.5
 NAS-Identifier = <not present>
 Called-Station-Identifier = 5300
 Calling-Station-Identifier = <not present>
 Client-Friendly-Name = Cisco 5200
 Client-IP-Address = 172.17.101.5
 NAS-Port-Type = Async
 NAS-Port = 8
 Policy-Name = <undetermined>
 Authentication-Type = <undetermined>
 EAP-Type = <undetermined>
 Reason-Code = 16
 Reason = There was an authentication failure because of an unknown user name or a bad password. 

Look at Username !!!, it would be my human username and not that !
Thanks for any comments.
Regards.