Same here.

One recent reply was "our system redirected you to another survey after you finished, hence the error message"

Yes they pay up once you email them. But the frequency of happening is getting absurd - I sent them the requests on 3 surveys 2 nights ago that was not including those $1-$2.5 survey that disqualified me way beyond the initial time stated. I started to keep track of time and take screen shot when there was a bar to indicate how much completed.

Their system is having serious issue, or, this is deliberately designed so they pay out much less while still produce the survey results they are contracted to get since many would just not take the trouble to write them.