Adding ASCX file with SharePoint WSPBuilder Project

You can't add a new ASCX file in a WSPBuilder project. To enable it you should modify your CSPROJ and modify the ProjectTypeGuids.

<ProjectTypeGuids>{349c5851-65df-11da-9384-00065b846f21};{fae04ec0-301f-11d3-bf4b-00c04f79efbc}</ProjectTypeGuids>