Explanation/Reference:
Explanation:
By default, sandboxed solutions are disabled. Enable sandboxed solutions on every application server on which you want to run sandboxed solutions.
Note:
To enable sandboxed solutions by using Central Administration
Verify that you have the following administrative credentials:
1. You must be a member of the Farm Administrators group on the computer that is running the SharePoint Central Administration Web site.
2. On the home page of the Central Administration Web site, in the System Settings section, click Manage services on server.
3. On the Services on Server page, in the Server box, select the server on which you want to enable sandboxed solutions.
4. In the Microsoft SharePoint Foundation Sandboxed Code Service row, in the Action column, clickStart.
5. Repeat steps 3 and 4 for each server on which you want to enable sandboxed solutions.
Reference: Enable sandboxed solutions on the farm (SharePoint Server 2010)