chatsystem problem

HI all, i made a chat system with php and mysql , it works, thats the good thing, but after 30 seconds an php error message appears. Please help. I did it this way: one mysql database with one entry containing the message 2 frames one with the input one with the output i think the input is ok but i have trouble with the output it starts with the frame PHP file chat.php <HTML> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel=stylesheet type="text/css" href="format.css"> </head> <body> </body> </html> <?php require("chat4.php"); requires the chat 4 file below ?> chat4.php: <?php $db=mysql_connect("localhost","$benutzer","$passwort") or die ("Konnte nicht verbinden"); // writes the message in an variable mysql_select_db("abi")or die ("keine datenbank"); // writes the message in an variable $result = MYSQL_QUERY( "SELECT inhalt FROM nachricht WHERE (art = 'gesamt')"); // writes the message in an variable $row = mysql_fetch_row($result); // writes the message in an variable if ($oldrow!=$row) // if message in mysql not old message he writes the new message { $oldrow=$row; // if message in mysql not old message he writes the new message echo $row[0];echo"<br>"; // if message in mysql not old message he writes the new message } mysql_close($db); include("chat4.php"); // he includes the same file so that he does the same thing again ?> ps an endless repeat doesn't work, too please help