Error with Push to Kindle from Pastepad

I’m trying to push a large (reformatted) text file to Kindle. I’m getting the same error in 2 different scenarios:

Scenario 1: Push to Kindle from Pastepad
After I paste the file in, PtK tries to preview it for me. I get error in the preview panel:

An error occurred.

Sorry, the page you are looking for is currently unavailable.
Please try again later.

If you are the system administrator of this resource then you should check the error log for details.

Faithfully yours, nginx.

When I try to Create EPUB instead of pushing to kindle, I get a new web page with the same error text as above.