I can only add one row to a table. Why?

[multimediocrity]

I have a database full of many tables. They're all working fine. However, on this one table, I can only add one row. As soon as that one row is added, I cannot add any more rows. Why?

Here's the script I'm using:

mysql_connect($dbserver,$username,$password);
$v_dbLink = mysql_connect($dbserver,$username,$password);
mysql_select_db($dbname);
$v_TheQuery = "INSERT INTO `supervisors` (`id`,`supervisor`,`supervisee`) VALUES ('', 'aaa', 'bbb')";
$v_TheResult = mysql_query($v_TheQuery);
$v_NumberOfRowsInserted = mysql_affected_rows($v_dbLink);
mysql_close($v_dbLink); 

[multimediocrity]

OH! Auto-increment wasn't set! Wow, why do I only find my answers after I ask for help? :P