Windows cannot find fsdfu.sys when attempting to upgrade the Highway firmware
This error normally occurs when the downloaded driver fails to extract correctly from the Highway firmware package - resulting in Windows being unable to locate the driver and identify the Highway when starting its Found New Hardware Wizard.
Download a compression tool like WinRAR (http://www.rarlab.com/) and extract the contents of the downloaded Highway firmware package to a folder of your choice. You can do this by right clicking on the package and choosing the 'Extract To...' option.
Once extracted, run the Pure Highway firmware download as normal and when Windows requests the driver then manually direct the Windows Found New Hardware Wizard to the folder to which you extracted the contents of the Highway package. Windows will find the correct driver and now be able to properly identify the Highway radio. You should now be able to continue with the update process.