Assuming you don't have another instance of the server software running, this could be caused by another application that is scanning COM ports and effectively blocking the VU1 server from being able to communicate with the HUB.  If you have another device installed on your system with some control software (even something like RBG lighting), the best way to determine if that is the cause of the problem is to disable it and try again.
Below is a list of software that is known to cause this issue
SignalRGB
If you identify any additional software that is causing this issue, please take the time to share it with us so that we can inform other customers.