Transaction suddenly not working

I know recently the server was update from PHP 4.3.8
to 4.3.9 but that shouldn't have effected anything.

Code:

$query = "INSERT INTO table1 (ProfileID, LurkID,
ProfileName, Edu,..................."
VALUES (null,......................."

ProfileID is the PrimaryID (autoinc) - I've set the
input value to null for the auto-inc to properly work.
I assume this is correct and it did work at one time.

Then before the next query:

$LID = mysql_insert_id();

Then each subsequent query uses $LID in the subsequent
tables.

However $LID is now returning 0 and the transaction
fails.

At the end of the transaction I follow through with
this:

//resx = all the queries
if($res1 && $res2 && $res3 && $res4 && $res5 && $res6
&& res7  ) // If all results are true
{
commit();
//echo "your insertions were successful";
unset($all session variable, $LID, );

}else{

...................

Puzzling since this script was working great. We did
also upgrad MySQL from 4.0.21 to 4.0.22-standard

Thank you,
Stuart