My hosting provider upgraded PHP to 4.4.0.
You need to upgrade your SMF.

http://www.simplemachines.org/community/index.php?topic=41955.0

It's just simple... edit Subs.php and look for
= &mysql_query

remove &
= mysql_query

Also....
edit mambo's index.php, look fot header(... and add the condition "if (!headers_sent())"

if (!headers_sent()) {
header( 'Expires: Mon, 26 Jul 1997 05:00:00 GMT' );
header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s' ) . ' GMT' );
header( 'Cache-Control: no-store, no-cache, must-revalidate' );
header( 'Cache-Control: post-check=0, pre-check=0', false );
header( 'Pragma: no-cache' );
}

Nope, no good... back to the drawing board. This time a whole heap of different login errors and one headers sent error from SMF 

Scott