Hi David, I had the same problem on a Canon Rebel T3i.
Here is the solution I found for my camera:
as you all well know, the shutter is made by 2 separate sets of curtains. When pressing the button one set would freely move while the other set would get stock triggering error 70 . I send my Camera for service to a local Camera shop who repaired it, replacing the shutter blades, for less than $ 200.00. I got my Camera back and it works like brand new again.