What did I do wrong? MGA Windscreen

["Simon Matthews" <simon_atwork@hotmail.com>]

I just finished replacing the right hand hood bracket on my MGA windscreen. 
As I tightened the very last screw, I broke the left hand bracket. What did 
I do wrongly, or are these particularly prone to breaking?

The brackets I am talking about are the right-angle brackets that hold the 
pin to which the hood rail is attached when the hood is put up. The bracket 
is also the attachment point for the top frame rail of the windscreen.

Simon