Ok thanks for the information, at least I know it comes from me 
I’ll fix it.
EDIT: I just tried with IE and it didn’t work, I’ll try with Firefox.
EDIT2: Same problem with Firefox and I tried on 3 different computers sharing the same internet access. Might come from my DNS or something on my box I believe.
EDIT3: Ok I found out where it came from. I added several special characters to the questions of my poll, noticeably ’ and : . : is fine but if I add ’ to one of the question, I suddenly can no longer create a poll (I’m redirected to a blank page). If I don’t add ’ the poll works fine. I’m French and using a French keyboard.