How to get rid of "Page Not Found" problem when uploading?

Try the "add it" option. After clicking on "upload" you'll find it on the right. And when the movie appears on the auto fill side click on it and then choose "Create". Sometimes the site gives you " Imdb ID already associated with this movie". Then you can easily click on the suggested titles of the same film you're looking for and upload the subtitles. If it is not there then you'll need to actually create it and upload your subtitle.

Hint: Try searching the movies by their original titles, sometimes that works better.

Thank you very much. But, that was not my problem. I can find the movie/series title. The "Page not found" error appears after finding the title, when I want to upload the subtitle in the movie's page. In fact, I think it is something about site traffic.