I've been having this problem too. I'm planning to call today.
I emailed them and they got back to me! Here's the message I received from PTCAS:
You can follow these steps to enter in your
reference's information:
Open a new reference request
Enter the first and last name
Skip email address
Enter due date and personal message
Enter waiver and contact choices
Come back to email to enter it BUT copy and paste the email into the box
-if you type the email in, it will give you an error
Once you paste the email you should immediately select “save this reference
request”
It should process you through to the next screen.
Hope this helps!
I actually just ended up asking my reference if they had another email and they did, so that may be another option. Good luck!