First, make sure the most recent version of LoggerNet is being used. (Improvements were made between versions 4.0 and 4.1 that resolved some issues with LoggerNet and some USB-to-serial cable drivers.) Next, ensure that the most recent drivers from the cable manufacturer are being used. Often, newer drivers are developed for devices after they are released, and the software shipped with those devices is not updated. The drivers can be downloaded from the manufacturer's website.