While playing with a possible patch for CONTRIB-1085, I noticed the following line:

print_error('mustbeloggedin');

There is no string or documentation page for mustbeloggedin. I played with the idea of simply using 'loggedinnot'; however, there was a comment in print_error indicating that it is best to have the string defined in error.php rather than relying on the backwards compatible option to look in /lang/en_utf8/moodle.php.

We should also go ahead and create:

http://docs.moodle.org/en/error/moodle/mustbeloggedin

I'll attach a patch with the new language string.

Peace - Anthony