base64 appears to do nothing?

Hi, I have an odd problem, i am trying to do basic authentication but the string does get encoded and the function appears to die.

Titanium.API.info('about to base64encode');
    var authentication = 'Basic ' + Titanium.Utils.base64encode(username+ ':' + password);
    Titanium.API.info(authentication);

The second info does not happen and the rest of the XHR function does not happen.. no errors in the debug console .. i have not seen anything posted on here and there are no apparent bugs with base64 encode..

Any suggestions... SDK 4.3 and Appcelerator 1.7

Thanks,

Jez