[Milhouse]

Any ideas what I've messed up? cheers

Doesn't look like you're communicating with the Kodi webserver but instead some other web server on whatever webserver.port is configured (default is port 8080).

Make sure webserver.port in texturecache.cfg matches Services > Web server > Port in Kodi Settings. And that you're communicating with the correct device (xbmc.host - default is localhost).

Edit: If you add @logfile=c:\tc.log to your command line, you'll see the data response from the webserver in the log file which may give you more of a clue what service you are communicating with.