There are a few possible reasons this happens:
1. Bad luck, got a wonky survey...either it is coded wrong, or they put the qualifiers late in the survey as opposed to the first few (I hate when that happens!).
2. Timing. Surveys have built in hidden timers. If you exceed what they think is a reasonable time...that you are going too fast...it will think you are not really paying attention and boot you out.
3. You missed a test question. These are hidden throughout surveys to make sure an actual human is reading and not just going along clicking a bunch of check boxes or radio buttons. This might be a question like, "please select the check box all the way to the right" or "This restaurant gives away free food all day".
Note: When you get the screen, "Sorry. You didn't qualify, blahbityblahblah, come back tomorrow." You can come back anytime. They load surveys all day. Sometimes you will get one 5 minutes later, sometimes hours later. Depends on when you have time to check back. It is not a one try and your done for the day thing.
Just make sure when you try back you are using all the same demographic info and email address.
I also didn't realize you could try again later in the same day. Thanks for the tip! 
