I had a similar problem before. The way to solve this is the following. In order to create a newsletter template you need a component under the apps/[youwebsite]/components folder and a template under the apps/[youwebsite]/templates folder.
1-On the template folder, select your template (in CRXDE or CRXDE Lite) and add the following property:
2-In CRXDE Lite navegate to content/campaings/jcr:content and edit the value of the cq:allowedTemplates property. Click the + sign at the botton of the dialog and and add the path to your template apps/[youwebsite]/templates/newsletter
I hope this could help