Posting errors

Hi guys.
I can not post any answer in my thread.
Whenever I tried to reply back to some comment in my thread, error occurs and the whole window just disappears.
What should I do?
I can not post anything in my thread right now because of this error.
Please advise me how to solve this problem.

Try using an incognito window ( google chrome ), or delete the cache and cookies.

Thanks a lot.
I appreciate your help.