I can't insert a drawing into my template

Determine whether it is the DRAWING or the TEMPLATE giving you troubles

Ensure You're Properly Inserting a Drawing into a Template

If your template accepts another drawing, the issue is the DRAWING
To confirm the problem is the DRAWING, insert a different drawing into that template and recreate the drawing that is giving you trouble.
If the template is not accepting any drawings at all, then the issue is the TEMPLATE.