When Tumblr gives you an error while adding a new page to your blog, you can fix the problem by simply creating your own page link in your theme's HTML code. This problem is a result of your theme's lack of support for page links -- you can still create a new page from your blog's Customize page, but you have to add the links yourself.

Step 1

Click "Customize" on your Tumblr dashboard to access your theme settings.

Step 2

Click "Add a Page" in the Customize pane to open the Add a Page panel. Although your theme may not support adding page links, you can still create the page from this panel.

Step 3

Enter a page title, and then enter your page contents in the lower portion of the panel.

Step 4

Replace "url" at the end of the Tumblr URL in the panel with a word that describes your page contents. For example, if you're creating an About page, change the URL to "yourusername.tumblr.com/about". (Use your own Tumblr username in place of "yourusername".) Copy this URL for later, when you create the page link.

Step 5

Switch off the toggle next to "Show a Link to This Page" to avoid getting the error message.

Step 6

Click the "Save" button to create the page, and then click the back button in the Add a Page panel to return to your theme settings.

Step 7

Click the line inside the Description box at the place you want to insert your page link, and then enter the following line of code on a new line:

<a href="PageURL">Page Title</a>

Step 8

Replace "PageURL" with the page URL you copied earlier, and replace "Page Title" with the word you want to use as your link in the sidebar. If you're creating a link to your About page, for example, the code should look something like:

<a href="yourusername.tumvlr.com/about">About Me</a>

Step 9

Click "Save" and then "Exit" when done.