WP Upload not working for one user

I just installed a multi-site wordpress site on a linux server – recently another admin is saying that he is having problems uploading files getting the error “Unable to create directory wp-content/uploads/sites/7/2013/05. Is its parent directory writable by the server?”. However, my account can upload media fine, as can another test account I created. Any idea why this may be occurring? the uploads folder is owned by the user and group apache, and permissions are set to 755.