Edouard,
I have an almost identical problem.
I migrated my WC files from a Macbook Air to a Mini. The Mini is connected to a Weather Envoy, which I configured using Weatherlink Mac.
Weatherlink Mac sees the Vantage Vue, and gets and displays data
But WeatherCat gives the same error the OP is getting.
I've checked to make sure the USB driver is correct for the OS X version on the Mini.
After two hours of troubleshooting, I'm running out of ideas.