Are you seeing a message like this?
If so, then it is probably because one or more of your questions has some critical information missing.
Its easy to find the questions that are incomplete, just look for a red tab next to the question (in the questions list). If you hover over a question with errors, it will show you what is missing.
There are 2 possible errors (please see the image above):
1. At least two options are required: A minimum of 2 of the options need to be filled.
2. Mark correct answer: You also need to select which answer is correct by clicking on one of the boxed marked "Incorrect" (to make it the "Correct" answer)