When you create a sand boxed solution for SharePoint 2010 in Visual Studio 2010 and try to deploy the solution , you could get the error “Error occurred in deployment step ‘Retract Solution’: Cannot start service SPUserCodeV4 on computer”(See the Picture1 below). In order to fix this , you need to go to Central Administration -> System Settings -> Manage services on server and start service “Microsoft SharePoint Foundation User Code Service” If you are developing SharePoint on DC(Domain controller),you need to check the solution from my previous post.

Error message.(Picture1)

Locate Microsoft SharePoint Foundation User Code Service.(Picture 2)