Twitch had an API change requiring you to have Client-ID in the headers.

Code:
JSONOpen -ud %v https://api.twitch.tv/kraken/streams/ $+ %caster

needs to become
Code:
JSONOpen -uwd %v https://api.twitch.tv/kraken/streams/ $+ %caster
JSONUrlMethod %v GET
JSONUrlHeader %v Client-ID: [YOUR CLIENT ID]
JSONUrlGet %v


You can get your Client-ID for your application on the connections page on Twitch.

https://twitch.tv/settings/connections

In the Developer Applications your program should be there, if not, just sign it up. I also believe that SReject does have this in his mTwitch applications.