[PHP-INSTALL] mysql_num_rows error message

[Afgin Shlomit]

I install a new solaris computer with
apache 2.0.48, mod_perl 1.99_12, Perl v5.8.1, PHP 4.3.3, MySQL 4.0.15a

We have a program that use php. it work on the old server with php 4.1.2,
apache 1.23, MySQL 3.23.49. When I run the program on the new server I got
the following error:
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result
resource in /path/to/php/script/file.php on line 43

Any Idea why it happen?
        Shlomit.