I got the error message as well, though I think it said I had completed the survey. Also had problems getting into the survey. I guess we all got the email round the same time and have been hammering their server.
I couldn't get into my account, though I have now just tried again and it has let me in. At least it confirms that I did complete the survey for my 300 points. This is after I emailed them about the problems.
I also asked them how we can complete the 2 surveys by 31/7/15, given that it is now 7.00pm AEST on the 31st. I asked if they were sending another survey, and would I have to wait up until midnight so that I can complete it in time to qualify. 
I suspect I will get no answer from them!
