m (Protected "404.shtml": this "system page" should not be moved [edit=sysop:move=sysop])
If an internal page link lead you here it may either contain invalid characters or the string "index.php", which is known to cause trouble.
If you are sure the page exists because you followed a "blue link", change the URL in your browser's address bar from
http://docs.joomla.org/index.php?title=Page_name_causing_trouble The target page should appear.
First of all: don't try to move/redirect the page as this will not necessarily resolve the issue if the original page title is still linked to from someplace else.
Here's how you can fix links pointing to a bogus pagename:
If you clicked on a "red link" then the target page does not appear to exist. Here's how you may fix that:
Post the issue in the Developer Documentation forum, or if you don't have an account for the Joomla! forums (how comes?) leave a note on the talk page. Please sign your entry by adding four tildes ~~~~ or click the "signature" button in the editor's toolbar.