Bug??? "Duplicate entry '255' for key 1 " on auto increment

Hi All, I have a table problem with "Duplicate entry '255' for key 1 " when any of my auto increment rowID fields reaches 255 I have installed PHP Version 5.1.2 and mySQL 5.0.11-beta on Win XP Pro. Each table in my DB that uses an auto increment for rowID fails at the 255th record insert. I have redefined the field: TINYINT, INT, VARCHAR, ... Same problem on several files. They all work OK until I hit #255 Is this a bug? Have I defined my table improperly? Is there a fix? TIA, Mark Here is my table defn: $query = "CREATE TABLE $table_name ( rowID INT UNSIGNED NOT NULL AUTO_INCREMENT, category VARCHAR(25) NOT NULL, trans_type VARCHAR(8) NOT NULL, PRIMARY KEY (rowID))";