Error initializing sessions directory
FireStats requires write access to a directory to store session information, in normal circumstances FireStats creates the directory fs_sessions inside the temp directory, but if the server is configured to use PHP safe mode then using the temp directory directly may not be possible.
in such cases, FireStats attempts to use the directory fs_sessions under the FireStats home directory (for example, /www/firestats/fs_sessions).
You need to create the directory for FireStats, and grant the PHP user write access to it.
exactly how to do it highly depends on your server configuration. if you encounter problems please consult your system administrator.