The most common causes are:
1. You're not using the email you signed up with. If you get the "Unknown email" error, the email you're entering is not the one you used to created the account.
2. Emails from PixelPeeper go to Spam. Check your spam folder and add [email protected] to whitelisted contacts. The specifics of how to do that will depend on your email provider.
3. Your browser is outdated. Make sure your're using the latest version of your browser. Supported browsers are: Chrome, Firefox and Safari. If you're using Internet Explorer, the site won't work for you.
If the tips above didn't fix the problem and you still can't log in, email me.