If you a "PHP Fatal error:  Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away'" error message in your Apache error log while trying to upload a file in SimpleRisk, then the issue is likely due to the max_allowed_packet setting for your MySQL server being set too low.  Try changing it to 16777216, restart MySQL, and see if the error continues.