I have a quite empty local instalation of Moodle 1.8.3+ (updated just now) and of Moodle 1.9 beta 2 (updated just now).
In moodle 1.8.3+
In server->Debugging I have Debug messages = ALL
I have only the Miscellaneous category with 6 courses inside.
If I go to Site Administration->Corses->Add/edit courses I get a page showing the list of categories (only "Miscellaneous" in my case) but showing two errors at the same. They are:
Notice: Undefined variable: category in /Applications/MAMP/htdocs/moodle18/course/index.php on line 304
Notice: Trying to get property of non-object in /Applications/MAMP/htdocs/moodle18/course/index.php on line 304
If I try to "Add a new course" I get "Either course id or category must be specified"
If I get inside the Miscellaneous category I don't get any error and if I try to "Add a new course" no error is risen, too.
Again, if I try to "Add a new course" from inside the Miscellaneous category I don't get any error.
All is as if in the first action I am trying to create a course out from the the unique category, and, of course, this is not allowed (I would like to get this too, but this is a different topic).
Whatever I told you now IS NOT TRUE in moodle 1.9 beta 2. There all is right.