If when you upload a solution to the solution gallery in SharePoint 2010 you receive the following error. "This solution contains invalid markup or elements that cannot be deployed as part of a sandboxed solution. Solution manifest for solution '64afe4f8-6a99-42e8-9845-43fc18cc49f8' failed validation, file manifest.xml, line 10, character 4: The element 'Solution' in namespace 'http://schemas.microsoft.com/sharepoint/' has invalid... Continue Reading →