Here is the problem:

====================
:~/tmp/darcs> mkdir two\ words
:~/tmp/darcs> cd two\ words/
:~/tmp/darcs/two words> darcs init
:~/tmp/darcs/two words> cd ..
:~/tmp/darcs> darcs get "localhost:tmp/darcs/two words"
Invalid repository:  localhost:tmp/darcs/two words

darcs failed:  (scp) failed to fetch: localhost:tmp/darcs/two words/_darcs/inventory
====================

Here is how I solved it for myself (a darcs patch):

===================
{
hunk ./External.hs 188
+                 tr ' ' = "\\ "
}
===================

I imagine that copySSHs might also need some change.