WordPress 3.1 WP_Query stopped working

upgraded to 3.1.. using the Devster theme. The slideshows and another special post query stopped working..

this variable ends up empty.. even tho posts do 开发者_StackOverflow社区exist in that category..

$featured_slide = new WP_Query('category_name='.$featured_cat.'&posts_per_page='.$featured_num);

Any help? I didn't see anything that would change this behavior.

I just started learning WordPress and am a beginner php programmer. I was testing the loop examples that were given in the WP's Codex Loop section. I typed in the example code to get only one post from the "feature" category and received a fatel error that there was no valid class. I ended up just playing around with it and changed the $WP_Query to $wp_query. This gave me another error about being empty. This error had something to do with the $do_not_duplicate line, so I just deleted this one. Not sure what is empty because my category exits with 2 posts added to this category. At least it seems to be working now that I have deleted this line. It's very frustrating for a newbie. I hope this helps.