Add New Page

After clicking add new page, I got this Warning message right above the page:

Warning: Creating default object from empty value in ................\.........com\wwwroot\wp-admin\includes\post.php on line 494

Then, after I typed a page title and clicked on the Submit for Review (previously Publish button), I searched for the newly created page but I couldn't find. I guess this means the page was never created. Help!

Please check if same happens on default WP theme. If so - I would suggest to reupload all the WP files as there might be something wrong with them.

I don't understand what you mean exactly. Do you mean I have to redo everything right from the very beginning? Can you pls explain with more details? I've already added pages before except this time that I have this problem. I've put so many contents already into the site.

Wordpress comes with default themes - change to default WP theme to test if the problem is caused by our theme or by WP itself. If second - you need to fix your WP installation.

After changing to default WP theme, I can Add New page and Publish it without a problem. What do I do next in this case?

Have you started with quickstart or standard template?

I started with Quickstart then updated it to the updated version sometime last month.

Sorry I made a mistake. I switched the themes with a different website I am also currently doing. But the website where I have a problem with Add New Page, I couldn't even switch themes. It just stays as the Creativity theme. Help!

It looks like a server related issue or your files are damaged.
I would suggest trying to reupload entire quickstart again and override all the files.