This one is quirky. If you've checked your Error Console, examined your code to make sure the proper element is being used and have done every other troubleshooting tactic out there, then the answer is probably the following:
You can't assign the submit button name attribute equal to "submit".
Crazy, right. Well, see for yourself!
<form action="">
<input type="submit" value="blah" name="submit" />
</form>
<form action="">
<input type="submit" value="blah" name="othername" />
</form>
$('form input').submit();
You'll be amazed to find that only the second form will submit.