Kinda annoyed by the error pages these few days.
Firstly it was the 500 internal error, then it was the 404 error.
I hate that word.
Full of errors that I don’t know how to fix.
So finally what I did was upgrading the WP,
then change the Permalink structure back to the default style.
(wasn’t able to do that before the upgrade… so I guess upgrading did help a bit)
So long as the pages can be displayed, I’m okay with it (for now).