Control.com - Nerds in Control

We have installed new software for Data Acquisition from Real Time Ambient Monitoring Stations AND we are having problems... Briefly the system is as follows:

A local ADAM Data Acquisition Module collects data from Ambient Analyzers and passes the data to a local PC on RS232 port... The software used is ENVIDAS which collects the data from ADAM and displays it.

Additionally, for remote viewing of data an Internal Modem is installed in Local PC running ENVIDAS and connected over a telephone line to a remote Modem in a PC running an 'ENVIEW' software.

Enview Polls automatically at a set interval of time and connects with remote modem and collects the data.

Problem: Remote PC dials the local PC, local modem detects the 'Ring' but after some time stops the communication giving a 'No Carrier' Message.

What are the possible causes of No Carrier Message?

Our observations:
The software, the vendor says, is time tested and running successfully at many locations without a problem.

Our telephone lines are noise free... No palpable noise is noticed during telephonic conversations.

The Modems have been changed and three different makes have been tried... but the No Carrier Message appears frequently and communication stops.

Can anyone help us troubleshoot this problem??

au revoir
Rahul