I will explain how to:

Use Geocator's Auto Cookies MOD to automatically fix cookie settings
Manually configure the settings by directly editing the config table in the database
These are some "symptoms" of incorrect cookie settings:

You are redirected to a blank page or 404 page after logging in, but if you click back, you are logged in
You are redirected to a blank screen or 404 page when trying to access the administration panel
You have to enter your username/password more than once to successfully login
You are redirected to other locations when logging in or entering the administration panel