Z-Wave stick Aeotec "Error connecting to device. No Ack" message

Hello, 

I'm using ComfortClick servers, but because I had a problem with one of the servers, I had to go back to a windows machine for a few days. 

Since I was using a Z-Wave Aeotec stick on the ComfortClick server, I thought it would be straightforward to use it on the PC : just plug and play.... well, not at all. I got the following message each time the server attempted to send a message to the stick "Error connecting to device. No Ack". 

It was driving me mad... I tried all kind of settings, and eventually found the solution - so just posting the question and the answer in case you face it so that you don't get crazy. 

When connecting the Z-Wave stick, Windows (7) is installing automatically the standard USB to COM drivers. But they are no good for the Aeotec stick. Some special Aeotec drivers must be installed in place of the standard ones. They can be found on 

https://help.aeotec.com/support/solutions/articles/6000034892-z-stick-gen5-drivers-inf-files

This fixed the issue :-)