$sql = mysql_query("SELECT id, firstname, lastname, phone, cellphone, email, starttime, finishtime, event FROM calendar WHERE MONTH(starttime) LIKE '".$eventid."%' ORDER BY starttime ASC");
Seems to bring back zero rows when there are 2 rows iin he database matching the 5th month.
MONTH() returns a number between 1 and 12. LIKE is a string comparison function.
Therefore MONTH(starttime) LIKE '".$eventid."%' is like e.g '12' LIKE '2007-05-11%' and that will never match.