There's an earlier note here about correctly referencing elements in $_POST which is accurate.  $_POST is an associative array indexed by form element NAMES, not IDs.  One way to think of it is like this:  element "id=" is for CSS, while element "name=" is for PHP.  If you are referring to your element ID in the POST array, it won't work.  You must assign a name attribute to your element to reference it correctly in the POST array.  These two attributes can be the same for simplicity, i.e., 
<input type="text" id="txtForm" name="txtForm">...</input>