Membership Plugin - Default Register Page is "Empty" after Upgrade

Hello. I have just upgraded to the latest version of Membership Premium, but this seems to have introduced a problem: the default Register page is empty. This was working fine before upgrading. Using Create Page has not worked; nor has deleting the Register page and then attempting to recreate with Create Page. I even tried adding the short code to the empty Register page, but all that did was bring up a white box around the word Register (which appears in black) on the screen.

Any help on how to get this part of the system running without re-installing everything would be most appreciated!