it is about "restriction on a page"

[박주현]

one of my colleagues can't see a page.

the error message is that "page not found"

I think the problem is related to restriction on a page.

How can I fix this problem? what should I do?

[Nic Brough -Adaptavist-]

I think you are right about restrictions.

You will need to find someone who can read the page (you maybe?), and get them to look at the red padlock.  That will show the restrictions for the page and hence tell you why your other user cannot see it.  You'll then need someone who can restrict pages in that space to change it.