Hmm... seems like folks aren't noticing what you're actually asking -- it appears $_SERVER['REQUEST_METHOD'] does not equal the method your form is submitting by.
Do you have any scripting that's trapping the onsubmit and trying to AJAX it? Have you tried echo'ing out the value in $_SERVER['REQUEST_METHOD'] to see what's in it when the condition fails?
Unrelated to your problem, but you might want to consider using semantic markup instead of tables for layout while at it... lose the table, get a fieldset in there, and get FOR attributes on your labels pointing at ID's on the INPUT. You may also find benefits to flipping your single and double quote usage.
Really though, if a variable does not contain a value you expect or a simple comparison is failing, echo out the failing var to see what it contains.