I note you are calling echo $_POST['jason'];
at the end of your script which I would expect to cause this error - just a typo in the question? You have it correctly as 'json'
earlier.
Update
Ok - think I see it:
Defined pcompensation:
<textarea name='pcompensation'/></textarea>
Reading it:
item.find("input[name=pcompensation]").attr("value",p.compensation);
Which should be:
item.find("textarea[name=pcompensation]").attr("value",p.compensation);
Same for your other textarea
custom fields.