By default, MediaLab requires that some data be posted from a custom item in order to continue. You get around this by adding a hidden variable or as one user recently suggested, you could simply add a value to the continue button. See:
www.empirisoft.com/Support/showthread.php?t=789

It occurs to me though that the solution might be a bit trickier in your case. In the link above, we were talking about a custom item which was not supposed to collect any data (as opposed to optionally collecting data if a response were made).

If you want to post your custom item and que file, maybe we offer some specific html code for you.