Hello MrJamesWeston,
The message “PackagingResults:Error: Error Unknown Command” is a general message that basically means “The packaging process failed” and doesn’t give any details. Whenever you see this message, you should be able to use Ctrl+F (Find) to search for the words “Error” and “Warning” to find out what is going on. In this case, it doesn’t seem like the entire log file was included so the “CrashOrAssert” mentioned isn’t shown here.
Also, can you please include the log file called “UnrealBuildTool-2017.01.22-19.45.24.txt” located at: C:\Users\UserName\AppData\Roaming\Unreal Engine\AutomationTool\Logs\