I had a problem with downloads not working correctly on multisite installations. Instead of the files downloading, they would open in a new browser tab.
From other posts, selecting 'force download' should resolve the problem.
But in multisite installations, this does not work, and instead returned "Download path is invalid!"
So I got in the code and tried to debug it. This is what worked for me:
1. edit download.php
2. around line 524 you will see:
$patterns = array( '|^'. get_bloginfo('wpurl') . '/' . '|');
$path = preg_replace( $patterns, '', $thefile );
3. add the following lines directly below this:
//for multisite installations
if ( is_multisite() ) {
$path = '/wp-content/blogs.dir/' . $blog_id . '/' . $path;
}
This resolved the problem for me. Hope it works for you - and I hope the developer adds this as a permanent fix!
good luck,
elaine