php error message [Fixed]

Hi,

I'm not sure how to describe this.. but i got this error message.

Warning: copy(/home/stefnitert/domains/managementplatform.nl/public_html/wp-content/blogs.dir/1/files/thumb.php) [function.copy]: failed to open stream: No such file or directory in /home/stefnitert/domains/managementplatform.nl/public_html/wp-content/themes/bp-social/includes/custom-functions.php on line 19

this is the url.
http://managementplatform.nl

Does anybody know what goes wrong here?
ty.