I am using SharePoint 2010 and creating a simple web part using Visual Studio 2010. When I create a SharePoint project in visual studio 2010, I specify "Deploy as a sandboxed solution" option. When I run the project, in a page in the SharePoint site when adding a web part I can see the web part. But when I try to add the web part to the page, I received this error "The sandboxed code execution request was refused because the Sandboxed Code Host Service was too busy to handle the request.".
I have searched on Google for the error message. The resolution to this error is to start the "Microsoft SharePoint Foundation User Code Service" service in the Central Administration. However when I look at the Services on Server using central administration site, I am missing this service. I don't see this service I was able to run the sandboxed solutions before but it is not working any more. I don't know how to fix this.
Best Answer
I fixed thus by going to Central Administration > System Settings > Manager user solutions. Under Load Balancing, I selected "All Sandboxed code runs on the same machine as a request" option and it is all working now.
For some reason I am still missing this service - "Microsoft SharePoint Foundation User Code Service". However I have always had "Microsoft SharePoint Foundation Sandboxed Code Service" service listed under Services on central administration site. And I am using SharePoint Server Standard Edition so it may be that for Standard edition I have this service instead.