Error Message after Installing Theme

I followed the installation instructions to the letter. But somehow, whenever I install some themes, including the Social Network Theme, I always get this message:
arning: file(/home/lsi/public_html/mtestwp.lsinteractive.net/wp-content/themes/bp_social11/style.css) [function.file]: failed to open stream: No such file or directory in /home/lsi/public_html/mtestwp.lsinteractive.net/wp-includes/theme.php on line 180

Warning: implode() [function.implode]: Invalid arguments passed in /home/lsi/public_html/mtestwp.lsinteractive.net/wp-includes/theme.php on line 180

When I preview the themes, what I see is a blank page.

Help. Really desperate. Don't know php. But I can follow instructions pretty well.