Ajax crash caused by lack of memory?

I have almost no experience or training in Ajax.  I was recently tasked with maintaining a C# MVC program that makes use of an Ajax call as the final step in the download process of a zip file.  It seems to be crashing when the incoming zip file has too many files.  As far as I can tell this is a conventional Ajax routine.  It has a 'Success:' section and an 'Error:' section. 

If the conditions are such that the system is working (just a few files),  I can put window.alert popups in the Success: section and observe the processing(inside the for loop, for example).  It the number/size of files is excessive (546 for example, in a 646 meg zip file) the system goes directly to the 'Error:' section without ever displaying my popups.

The errorThrown value is 'Internal Server Error'.  Beyond that I haven't found anything else so far.

Any suggestions for further troubleshooting?

The Ajax is as follows:

   $.ajax({
                url: url,
                type: 'POST',
                contentType: 'application/json',
                data: JSON.stringify({ ids: ids, themeId: themeId }),
                success: function (result) {
                    var form = $('<form method="POST" action="' + url + '">');

                    for (var i = 0, count = ids.length; i < count; i++) {
                        form.append($('<input type="hidden" name="ids[' + i + ']" value="' + ids[i] + '">'));
                    }
                    form.append($('<input type="hidden" name="themeId" value="' + themeId + '">'));

                    $('body').append(form);
                    form.submit();

                    $('.loader-wrap').hide();
                    $('.btn-pickup-download, .btn-pickup-download-all').removeClass('disabled');
                },
                error: function (XMLHttpRequest, textStatus, errorThrown) {
                    $('.loader-wrap').hide();
                    $('.btn-pickup-download, .btn-pickup-download-all').removeClass('disabled');
                    alert('The requested report(s) is unavailable. If you have any questions, please contact your Account Manager.');
                }
            });