Error function cannot be a directory

Hi I tried this on my blog (multisite) and it gave me this error

Warning: copy() [function.copy]: The first argument to copy() function cannot be a directory in public_html/ilocals/wp-content/plugins/wp-resources-url-optimization/wp-resources-url-optimization.php on line 129

http://wordpress.org/extend/plugins/wp-resources-url-optimization/