An assembly file (*.iam) is only a list of hyperlinks to the part files (*.ipt) and a record of assembly constraints (and a bit more).
You must include the part files.
I'm sorry, but I don't follow Are you saying that I should include the part files in an assembly together with plate and then combine it with the larger assembly? I tryed that but I found it difficult to get X grounded as I was moving the plate along the "treadmill". I need X to be "out of the picture" during the bend/flush process and then at last, get it mated with the plate to "complete" the product.
You posted a *.iam file.
Look at the file size? See anything unexpected?
An assembly file (*.iam) is nothing more than a record of hyperlinks to where the parts (*.ipt files) are located.
There is no geometry in an assembly - only tells Inventor where to find the parts (on your hard drive).
In order for an *.iam file to rebuild the assembly from the instructions in the *.iam the *.iam must have access to the part (*.ipt) files. You did not attach those files here.
You must attach the *.ipt part files here.
Missing OJOJ.ipt and xxx.ipt doesn't have dimensions and almost horizontal line - is that intended?