Are you using the online (web) form or the PDF form to collect your responses?
If it is a PDF form then you need to make sure people use Adobe Acrobat, Adobe Reader or Adobe Reder Mobile to fill out the form.
Apologies, of course!
I have uploaded a fillable PDF into Forms Central that has been modified for Acrobat Reader forms capability.
Please refer to : http://forums.adobe.com/docs/DOC-2653
If people are not using Acrbat, Reader or Mobile Reader to submit the data then it is possible that the submission will fail silently. There is no way to recover the data in those cases. The problem that third party pdf viewers don't support the full functionalities for pdf forms.
Ah, ouch! It’s a complicated form though; I don’t think it lends itself to a web form.