Why this $.post() does not call the target php function?

Why this $.post() does not call the target php function?

I cannot for the life of me see what is wrong with the $.post call. This used to work, so I'm baffled as to what caused it to break.

I am trying to use $.post() to pass two parameters, which are used to retrieve some data values in a database call, in the fetchAlleles.php script, then assigns them some id's in the page. When I step through the code using a debugger, however, I am unable to step into that script, and the variable "result" is never defined.

If anyone can point out the error, I would be most grateful; here's the code:

    $.post("fetchAlleles.php", {"mndx": mndx, "sndx": sndx},
      function(result) {
    $('#allele_1_1').get(0).value = result[0].allele1;
    $('#allele_1_2').get(0).value = result[0].allele2;
    $('#run_date1').get(0).value = result[0].run_date;       
      }
    );