Application service down due to SQL Server error
Before generating this message, the server would have previously received other structurally incorrect packets that corrupted components within the application stack.  This is typically how denial of service or penetration attacks are formed.  If you have this system on the Internet, I'd get it off the Internet, or use filtering to restrict access to specific IP's.  If it's not on the Internet, I'd check the users for software that has not been tested and qualified by an entity such a vendor or open source community.