The problem lies in a certain vagueness in turbotax' forms.
The charm for us was this: you need to keep a US address under "my information" the whole time until shortly before you actually submit - otherwise the whole thing doesn't work. But when you finally change the address there, make sure that you use the ISO code for "foreign county or state". It does obviously not ask for a CODE, but you must insert the code there, NOT the name of the county/state. Ours went through after three failed attempts.
