If you are developing any Sandbox solution for Sharepoint 2010, then you may have faced an error while deploying any solution to your development server. The error in Visual Studio 2010 output window looks like this generally:
Error occurred in deployment step 'Activate Features': This feature cannot be activated at this time. The contents of the feature's solution requires the Solution Sandbox service to be running.
The fix is simple. You must make sure that your "Sharepoint 2010 User Code Host" service is running. It is disabled by default installation. So, you have enable and run it. If you want to deploy the solution, then again you see the same error output. Actually, you have to make sure that this service's status is active in Central Administration Site. To see the status go to your Sharepoint 2010 Central Administration Application. Under System Settings > Manage services on server make sure that "Microsoft SharePoint Foundation Sandboxed Code Service" service is started. If it is stop start it. Now, you can package and deploy sandbox solutions right from Visual Studio.