Error after a while???

Hi, I have a database and a site which has members and so on...... but now I have service (also for a long time) http://www.wjp.cjb.net a guestbook service. But yesterday somebody mailt me to say that this error was on his guestbooksite: Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/k/l/klaassen/public_html/WJP/include/gastenboek.php on line 9 Warning: mysql_fetch_object(): supplied argument is not a valid MySQL result resource in /home/k/l/klaassen/public_html/WJP/include/gastenboek.php on line 28 I checked his table and found out that the table is empty. What could there be wrong with this line of code if a table is empty? And what can I do about it. It never accurred before and we tested this service a lot before we started using it, and then there wasn''t any problem at all when a table was empty. (PS all the fields in the table have the option that they are allowed to be empty.) M.B.