When i trying to create a sandboxed solution for SharePoint2010 in
Visual Studio 2010 and try to deploy the solution, i got the error
"Error occurred in deployment step 'Retract Solution': Cannot start
service SPUserCodeV4 on computer".
In Order To fix this error, do like this
go to Central Administration -> System Settings -> Manage services
on server and start service "Microsoft SharePoint Foundation User Code
Service".
Now try to deploy sandbox solution this time i didn't got any error.