Bug or ineptitude? Unexpected type error in Background.exit using makeImageRequest

Hi,

I don't _think_ I'm doing anything wrong here, but...

In my ServiceDelegate, I have code like the below (where "Stuff" sets the values I need...).

function onTemporalEvent() {
	////
	// Stuff...
	///
	Communications.makeImageRequest(url, null, options, method(:responseCallback));
}
// Set up the responseCallback function to return an image or null
function responseCallback(responseCode, data) {
	if(responseCode == 200) {
		Background.exit(data);
	} else {
		Background.exit(responseCode);
	}
}

And then in the console, I see...

Error: Unexpected Type Error
Details: Failed invoking <symbol>
Stack: 
  - responseCallback() at E:\APath\AClass.mc:70 0x10000224 

Where line 70 is:

Background.exit(data);

I mean...

SURELY there is nothing I can do wrong here? Or have I missed something about loading images with makeImageRequest?

Perplexed of Dublin