I run into this all the time.
A user cannot connect to Network Connect. The technician takes the laptop to another location and it works fine. All ISPs allow ESP and even if they didnt I should be failing over to NCP.
Our users are not doing anything weird. Dell Laptops, behind Linksys Firewalls running DSL.
Anyone else experience this ?
This may not help, but I have found enabling Roaming Sessions in Role Session Options made NC work on several AirCard situations where IP addresses seem to change.