The reason it wont convert/flatten is that that "bend" on the left isn't a true bend. It is kind of a bend and twist. You can see this easily by choosing the Inquire Element command -- it should be a cylinder -- but its not, its a bspline. So the question is -- is this supposed to just be a bent up plate?
If yes -- then you can fix the model using various surfacing and synchronous techiniques and it will convert/flatten. I did this in ST8 -- else I would send you the model.
If no -- if it really is supposed to be more than a "strap" in the flat and is a bent then twisted model, you will have to use "Create Blank" to get the shape. This command is only found in Solid Edge Classic and above.
Dan's diagnose is perfect! It seems this part is coming from catia or pro-e...
Here is a short video what I suggest doing "flattenable" part:
Too fast for me Imi.....I was just working on a example video of that very scenario, then spotted your response. As always, another job, VERY well done!
Design Manager Streetscape Limited
Solid Edge ST9 [MP5] Classic [x2 seats]