We all knew (or should have known) that this day was coming, but Microsoft has finally turned off the SharePoint Sandbox execution environment. This means that Sandbox solutions that contain code (event receivers, web parts, etc.) will no longer activate.
Solutions that contain only declarative (XML) elements, such as site columns and content types and list definitions/instances, are not affected.
If you need to provision/configure items in a site/web when features are activated, then CSOM is your friend. Patterns and Practices has code and cmdlets that can help.
Of course, you could always call your favorite SharePoint consultant. We can help. ;)