I have the same problem as you and I contacted the Questback directly. They checked it and told me, that the problem is because of the loop in the survey, using a very big list with around 1300 elements. So I can export the data as an excel file, but not as SPSS.
I hope, it helps you a little bit. If I were you, I would call Questback and ask them about your problem. Or you can send an email to Rhaya Ayoub firstname.lastname@example.org
- she was the one, that answered my questions.
I wish you luck with your survey!