Here is a tutorial on how to run the block in your vbulletin and I would beleive your error has to do with either your photopost table prefix has not been entered under Admin => Edit Integration or the file directly itself inc_ads.php the $link and mysql_select_db lines.
Do you see anything at all printing on your forum?
If you installed the plugin my suggestion would be to edit your forumhome template in vbulletin and add the line where noted below your $navbar call. The variable to print the block is $classifiedsfeature
Linear Mode
