I was stuck on this a long time while in my PDI. It seems like many other people have this issue so I'm going to post a work around I figured out.
Once you finish filling out your App Engine Studio app, instead of hitting submit and getting the same error click on the gear icon next to it. From the next screen scroll down and click "Open App in Dev Studio". This will bring you to the regular Studio app but it will also transfer all your tables, forms, experience etc. with it. From there you can close the window, your work has been saved in your PDI instance.
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