Create Custom Edit form for new content type based on "Video" content type.

Hello,

I was trying to modify already existing form for "Video" content type.
I created my new content type - derive from Video.Then i created new application page.Then I copied _layouts/15/EditVideoSet.aspx markup to my new page. I changed CodeBehind and Inherits attribute in (<%@ Page ... %>)
and I got following error :
Application error when access /_layouts/15/MyProject/MyNewEditPage.aspx, Error=Could not load type 'MyNameSpace.MyNewEditPage'.   at System.Web.UI.TemplateParser.GetType(String typeName, Boolean ignoreCase, Boolean throwOnError)     at System.Web.UI.TemplateParser.ProcessInheritsAttribute(String baseTypeName, String codeFileBaseTypeName, String src, Assembly assembly)     at System.Web.UI.TemplateParser.PostProcessMainDirectiveAttributes(IDictionary parseData)f6c4789c-ac76-f0ab-e8ef-49991281bfb7
02/28/2014 14:14:49.22 w3wp.exe (0x22EC)                      0x0B94 SharePoint Foundation         Runtime                      tkauUnexpectedSystem.Web.HttpException: Could not load type 'MyNameSpace.MyNewEditPage'.    at System.Web.UI.TemplateParser.GetType(String typeName, Boolean ignoreCase, Boolean throwOnError)     at System.Web.UI.TemplateParser.ProcessInheritsAttribute(String baseTypeName, String codeFileBaseTypeName, String src, Assembly assembly)     at System.Web.UI.TemplateParser.PostProcessMainDirectiveAttributes(IDictionary parseData)

Am I doing right, If i want to create copy of the EditVideoSet.aspx page?
If yes, what can cause this exception ?