The problem has been isolated to the X.25 network.

 Local System
 .----------.                                               
 |          |                                                
 |          |                                                Remote
 |          |                  X.25 Network                  System
 |          |            .---------------------.            .----------.
 |          +------------+                     +------------+          |
 |          |            '---------------------'            '----------'
 |          |                  ^          ^
 |          |                  |          |
 |          |                  |          |
 |          |                  |          |
 '----------'               The problem is here.