I've scoured the posts trying to find an answer to this and I have found many fixes but none seem to be fixing my issue. This just recently started occurring after we upgraded the wordpress version to 3.2 from another multi site version... both sites in the mu worked fine prior to the upgrade.
1.) I've double checked the .htaccess file and it is correct based on the examples posted... even regenerated it by updating permalinks
2.) I've added ob_clean(); to the ms-files.php file
3.) I've installed the Remove WordPress to WordPress filter
4.) double checked my upload path in the site settings: wp-content/blogs.dir/3/files
None of the above have worked.
Site 1: thepersimmongroup.com
Site 2: thepersimmongroup.com/speakers
Site 1 images work but Site 2 user uploaded images do not show...Any help debugging this would be appreciated.