GetSimple 3.0+ has a built-in security system to prevent CSRF. This will prevent attempts to create malicious cross-site attacks aimed at exploiting and/or compromising your GetSimple installation.
While, not recommended unless you are having problems: you can turn off CSRF protection (3.1+ only) via a gsconfig.php setting.
In rare circumstances, your GetSimple installation will give you false CSRF notices, and will not allow you to perform any actions such as saving/creating pages, deleting file, etc. This is a maintained list of reasons why this may happen: