Hi,
In case it happens to anyone , I found the problem , I cant reproduce it or pinpoint why it is happening , but it keep occurring from time to time .
here is how to solve the problem:
The folder "My Survey Attachments" holds all the images that you takes whether you submits the survey or not .
when you get the error go to this folder you will find one or more images that appear as blank , they just missing the suffix ".jpg".
Once you edit the image name with the correct suffix you can submit the survey , if you still get the error remove the image from the survey and reload it ,this time it will have the correct suffix.
iris