Troubleshooting network adapters on Windows

We all love the Internet and connectivity, but how often do we think about “how” we connect?

At work, I use a Windows PC, which has a physical Ethernet network adapter and a physical WiFi network adapter. Typically, I just use the Ethernet adapter, as it’s faster. I don’t need my desktop to use WiFi, unless I’m having to manage something on our wireless network. I recently noticed the desktop also has a Bluetooth adapter, but I haven’t used that yet, although an increasing interest in the Internet of Things means that I might start to use it soon!

In any case, that’s 3 network adapters. Already it’s starting to sound like a lot. But I also have a host-only virtual adapter for Virtualbox, so that I can have a private connection with my Virtualbox virtual machines. That’s 4 adapters now.

I also use a USB Maxon Modmax modem with a SIM card for connecting to a private network. That’s 5 adapters.

Recently, I’ve also started to use VMware on the same PC. VMware installs another 2 virtual adapters (host-only and NAT). That’s 7 adapters.

After installing VMware, I started to have issues with the USB modem, so I disabled those adapters, and everything was fine…

…until I wanted to use the USB modem in the VMware virtual machines, and to do that I needed the VMware virtual NAT adapter. So I tried that again and had the following result: “C-motech UI Main has stopped working.”


The Modmax connection would stay active until I dealt with that C-motech UI Main window. As soon as I clicked “Debug”, “Close program” or “X”, it was all over.

So I could have my VMware adapter and Modmax adapter enabled and achieve the network functionality I required… but I was blighted by this pop-up window that I had to try and hide on my screen. This wasn’t going to be a long-term thing I wanted to live with.


I called Maxon technical support to see if they had any insight, but they didn’t. The Modmax was also end-of-life years ago, so they weren’t going to work on troubleshooting it too thoroughly, which was fair enough.

So I decided to experiment a bit by disabling some other adapters and trying again… and voila it worked! I realized that the Modmax modem would work, so long as there was a maximum of 5 enabled network adapters (including its own adapter).

I can’t explain why this is the case. I’m guessing it’s a bug in the Modmax Connection Manager, but maybe Windows has some secret limitation… who knows? At the end, it matters that it works.

I rang Maxon back up to share my discovery, and that’s that. I’m writing this post in the event that someone else is Googling “C-motech UI Main has stopped working”. Hopefully my efforts will help them avoid this crash!


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