Apologies for the problems that you are obviously having with the competition entries. Our developers are aware of it, and are working on solving the problem, however they have a very cool new trailers pages that is being worked on first. The issue with competitions is, I believe, next on the list.
You could try deleting your cookies and seeing if that makes a difference - it might work for you - and can be found under the tools>options menu of your browser.
Again apologies for the problems that you are experiencing, and I hope that you are able to enter the competition you are interested in.