There are a few possible reasons why the mobile app may not recognize a physical answer sheet. When this happens, here are a few quick things to verify
1. Make sure that the quiz is expecting the physical form that you are scanning. The form name is on the 'Quiz Menu' and also displayed while scanning. The legacy forms are the 20, 50, and 100 questions form. If you are scanning a form other than the one selected, then the app cannot verify the form.
2. If you are using a custom form, be sure to select that form on the Quiz. Even if the custom form has 50 questions, you must select the custom form listed (including the matching 4 digit number). For a custom form to appear in the list on the quiz menu, it must have been created on your account on the 'Answer Sheets' tab or shared to your account by the teacher that created the custom form.
3. Make sure the paper is flat against a table top or other flat surface. If the paper is curling, use objects to hold down the margins of the paper.
4. A picture is worth a thousand words. If the above doesn't help, use the camera app on your device and take a picture of the problematic paper. Email it to us at firstname.lastname@example.org along with the name of the quiz you're grading and your ZipGrade account name. We can run it through some debug code to understand what's going on and hopefully a workaround.