Bug ?…and some help..

Hi guys,
just installed it and im impressed and love the design….
Anyway i think its a bug or nobody ever noticed?
When there isnt any post….(in the beginning for example) it gives an error like this….
But disappears as soon as the first story is posted.
————————
Invalid argument supplied for foreach() in /home/site/public_html/myblog/wordpress/wp-includes/template-functions-category.php
on line 304
No categories
———————————-
And i need a litle info on some things…
Are there more plugins,cause i was thinking about any type of guestbook?
And then all those import stuff,to bad that i cant find a simple what it is story so i understand what it is….
theres more but post them as they come… ??