Item9856: Improve error messages

git-svn-id: http://svn.foswiki.org/trunk/core@17594 0b4bb1d4-4e5a-0410-9cc4-b2b747904278
Item9856: Improve error messages

Also add the hint about the redirect hosts.

git-svn-id: http://svn.foswiki.org/trunk/core@17595 0b4bb1d4-4e5a-0410-9cc4-b2b747904278