I also had the same problem with the last version of WP (2.3.1). My solution is similar.
In the file wp-includes/plugin.php is the function remove_filter with this lines of code:
$r = isset($GLOBALS['wp_filter'][$tag][$priority][$function_to_remove]);
unset($GLOBALS['wp_filter'][$tag][$priority][$function_to_remove]);
I have added the ‘if’ to solve the problem:
$r = isset($GLOBALS['wp_filter'][$tag][$priority][$function_to_remove]);
if ($r) unset($GLOBALS['wp_filter'][$tag][$priority][$function_to_remove]);