I just managed to get into a weird situation with svn. One of my files seems 'lost' as far as the working copy is concerned. When I look on the server or do a fresh checkout of the containing folder in another location, the file is there, but in this one specific working copy it seems 'lost in space'.
svn status reports no changes (so not even a missing file)
svn update does nothing
I even tried re-exporting the file to my working copy, to no effect.
I would like to avoid having to resort to a fresh checkout of the whole working copy, if possible.
SVN 1.6.1 clients (including TortoiseSVN) had a bug where folders would sometimes erroneously be set to depth "empty". This causes the symptoms you describe. (Note that it's possible that the folder was made "empty" by svn 1.6.1 and has remained that way even though you've already upgraded to a newer svn client in the mean time.)
To fix it, use the "update to revision" menu item in TortoiseSVN and select the depth "fully recursive".