CAN bus troubleshooting. How?
One of the first things you should do is look at the bus signals with an oscilloscope, both individually and in differential mode. This will allow you to see whether the terminations are set up properly, what the bit period really is, and whether there are any noise, risetime or voltage offset issues.

The next step would be to try a CANbus analyzer tool, which will give further insight into any protocol problems.

It looks like the ICPCON device is designed to support DeviceNet specifically; does it support diagnosing the "raw" CAN messages?