"Page Not Found" error when clicking the page's link

We are facing with "Page Not Found" error when trying to reach a page through another page (which includes the link). I have permission and the page does exist. When I find the page link from page tree and click into it, there is no problem but, when I'm trying to reach it through another page's task list, I'm not able to. My teammates are facing with this problem, too.
From task list:
https://biesterfeld.atlassian.net/wiki/pages/viewpage.action?pageId=29131068?focusedTaskId=18
I've faced with.

My problem is about reaching to other meeting notes' page from a task list. For example:
https://biesterfeld.atlassian.net/wiki/pages/viewpage.action?pageId=29131068&focusedTaskId=18
on this page,there is a task, which appears on
"2015-02-23 Haftalık Satış Toplantımız" meeting notes and I want to use that link from the list.
I'm not trying to mark the task, I'm trying to go to the page that task appears originally.
We are not facing with this problem with all of the links which includes special letters, actually just on that task report.