This check determines whether the Microsoft SharePoint Foundation Sandboxed Code Service is started in the farm.
A Microsoft SharePoint Foundation solution package can contain custom code, features, branding, and different types of definitions and templates. SharePoint 2010 introduced a concept of the sandbox, which is basically a restricted execution environment in which custom code can run and access only limited resources. Thus, SharePoint prevents the custom code from damaging the rest of the system. Microsoft SharePoint Foundation Sandboxed Code Service is required to run sandbox solutions with the custom code.
Please note that sandbox solutions containing the custom code are deprecated as of SharePoint 2013.
Verify that the Microsoft SharePoint Foundation Sandboxed Code Service is running in the farm. To verify that the service instances are started and configured properly, go to Central Administration > Application Management > Manage services on server.
Additional information can be found in the following articles: