Testing the Windows XP publishing wizard

Some users are getting a file type error from the Windows XP publishing wizard when they try to upload any files, even ones we do allow. I've been poking around in the code and this seems to be being caused by the file having a content type that we don't recognise (I've quoted the code section here - http://www.livejournal.com/support/see_request.bml?id=639903).

I'd like to find out what content type we are getting but I have no idea how to go about that - anyone have any suggestions?

Edit oops - forgot not everyone can see that IC! The code is as follows:

function checkTransferManifest(xml) 
{ 
        var files = xml.selectNodes("transfermanifest/filelist/file"); 

        var validUploads = 0; 
        for (i = 0; i < files.length; i++) { 
                  switch (files[i].getAttribute("contenttype")) { 
                          case 'image/jpeg': validUploads++; 
                          case 'image/jpg' : validUploads++; 
                          case 'image/pjpeg' : validUploads++; 
                          case 'image/x-png' : validUploads++; 
                          case 'image/png' : validUploads++; 
                          case 'image/gif' : validUploads++; 
                          case 'image/tiff': validUploads++; 
                  } 
        } 
        if (validUploads > 0) { 
                  wizard.submit(); 
        } else { 
                  var helpText = document.getElementById('helpText'); 
                  helpText.style.display = "block"; 
                  window.external.SetWizardButtons(1,0,1); 
                  back = function() { 
                          window.external.FinalBack(); 
                  }; 
        } 
}