This may be because NetWorx skipped your network adapter due to a so-called 'physical' flag not being set. This is relatively common with USB dongle/broadband mobile modems, and as a result, the USB dongle is not present in the drop-down list of adapters to be monitored in NetWorx.
To work around this, please open the hidden settings as described on
this page, scroll all the way down and set
Physical adapters only to
False, and then restart NetWorx. Now you should be able to choose your adapter in the drop-down list of adapters and start monitoring its traffic.