Understanding ‘URB_INTERRUPT in’

I have a development board which, when I plug into the USB, appears on the PC as a virtual com port as expected. However most serial communication applications i try fail to communicate (one very old application does work).

Digging down the Windows Serial API reports that the connected device is not functioning.

Using Wireshark to monitor the port I continusly seeing the message: 6905 308.984603 2.4.1 host USB 31 URB_INTERRUPT in

What does this 'URB_INTERRUPT in' mean? Could this be the cause of my comms issue?

Thanks,