Tech2 communication error

[BigSilver]

2003 Suburban 2500, V8 6L:
When a Tech2 fails to communicate through the OBD output port of a vehicle, where as an OBD2 scanner does successfully communicate through the same connection port, what can one infer from this? (The Tech2 functions with other vehicles, so no it itself is ok.)

Any ideas?

[MrCritical]

Sounds like an oxymoron. Try another Tech2.