If you go directly to www.planapple.com and sign in there, the web site works fine. You only see this problem trying to use the Planapple Save Button while on some other web site.
Cause: you may have set your browser to block "third-party cookies".
Solution: allow third-party cookies for planapple.com. Either:
Un-check the "Block third-party cookies and site data" checkbox in your browser's privacy/content settings/cookie settings preferences
If you want to leave third-party cookies blocked for most sites, then add an exception that allows them for *.planapple.com