cms_folder/admin/inc/theme_functions.php line 230
$slugs should not be a $slug only? in debug mode $slugs throws an error, otherwise not.
It could be, yes, there have been some problems with menu_data(). Are you using the latest beta version of GetSimple or the stable release?
sorry, I forgot to write the version, currently I am using 2.01. And as the time passes by I am thinking if I did not make that bug myself, when saving file and not pressing Ctrl+S, but just S :-)