If u are using Your own Controls (.ascx) other than the default (view, edit & settings .ascx), then you need to modify some code in your Web User Control.
Let I have added a module named as MyModule1, and inside MyModule1 i have added a WebUserControl named Demo
Then go to DesktopModules >> MyModule1 >> Demo.ascx
open it's code behind file i.e. Demo.ascx.cs and replace the Inherited class named "System.Web.UI.UserControl" with
"DotNetNuke.Entities.Modules.PortalModuleBase"
Before replacing it will look like below:-
public partial class DesktopModules_MyModule1_Demo : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
}
}
After replacing it will look like below:-
public partial class DesktopModules_MyModule1_Demo : DotNetNuke.Entities.Modules.PortalModuleBase
{
protected void Page_Load(object sender, EventArgs e)
{
}
}