Are you using the link the the "Important Links" section to go to the Entry Form? It's at the bottom of the forum (above these messages) and looks like this:

Important Prep Links:

Sign up using the SIGNUP FORM  .
See assignments on the "2017 Prep Calendar" 
Log assignments on the ENTRY FORM  
Monitor your assignment progress on the 2017 LOG  
Compete in the "October Novel Prep Contest Rounds" 


Before Prep opens, I hyperlink the Entry Log to that error message.
After Prep opens, I hyperlink it to the Entry Form.

So either your computer is pulling the Prep page from cache (meaning it's an old copy of the page pre-dating 10/1 and it has the old link), or you're going to the Entry Form via some other means that I've forgotten exists, and I need to change the link in that location. Where are you clicking the Entry Form link?

Cheers,
Michelle