What is wrong when Open atrium is installed with no colors and images?
This is certainly a permissions issue on your temp and possibly also files directory. Go to admin/config/media/file-system and make sure that the directory set as your temporary directory exists, is writeable to the webserver, and is specified from your server's root directory. Also make sure sites/default/files and/or sites/[yoursite]/files (if using a multisite) exists and is writeable to the webserver.