Getting error while activating

Jun 13, 2016 at 3:28 PM
I get following error when activating the solution in SharePoint online.

Sorry, something went wrong
This solution contains invalid markup or elements that cannot be deployed as part of a sandboxed solution. Solution manifest for solution 'f377e24a-7159-4164-ac72-6d321382825c' failed validation, file manifest.xml, line 20, character 4: The element 'Solution' in namespace 'http://schemas.microsoft.com/sharepoint/' has invalid child element 'TemplateFiles' in namespace 'http://schemas.microsoft.com/sharepoint/'. List of possible elements expected: 'FeatureManifests, ActivationDependencies' in namespace 'http://schemas.microsoft.com/sharepoint/'.

What could be the issue?
Nov 30, 2016 at 7:25 PM
Same error.... Anyone have a fix?