Thanks a lot Phil for your help. It's OK now.
With SecureW2 and PAP on the user's PC and using ttls
I add these lines to my configuration:
Modules {
...
eap {
default_eap_type = ttls
...
gtc {
auth_type = PAP
}
ttls {
default_eap_type = gtc
}
...
}
...
}