consider the following repo layout:

Repo: Tools
/
|- trunk
|- branches
|- tags

And a local directory structure:
\Basedir
|--\Tools    (not under version control)
   |--\trunk ( checked out via 'svn co http://Server/svn/Tools/trunk /Basedir/Tools/trunk' )

When attempting to tag from my working copy via: 
% svn copy c:\Basedir\Tools\trunk http://Server/svn/Tools/tags/mynewtag

I get the following error:

svn: Commit failed (details follow):
svn: 'C:\Basedir\Tools' has no ancestry information

I assume that the working copy thinks that the parent directory is part of the WC.
However it definately is not, nor do I think it should be.

Also when I change the name of the parent directory from Tools to "Fewls" the svn copy works fine.

Any ideas?