Ok - I just went down the shed to look at the parts to see what you have to do.
While I was down there I realised I ws stupid in my previous post because if you cannot open the door you're going to have a hell of a time removing the inner panel. I took a couple pics while I was down there though so we can work out what we're dealing with.
I'm scared that if you cannot force it open somehow you may heve to remove the door skin very carefully trying not to crack the outer paint.
Have you tried spraying inox into any crack, recess anything you can get it into? You might be able to spray randomly through the top of the window hole if you wind the window down all the way. Maybe? Spraying inox like a madman inside the door isn't going to hurt anything.
In this pic you can see the mechanism that opens the door when you use the handle. (A) pushes down onto (B) and it released the door jam bolt.
This pic shows you cannot manually access the latch itself from the inside as it's got the sheaild around it.