How do you overcome the svn ‘out of date’ error?

I’ve been attempting move a directory structure from one location to another in Subversion, but I get an Item '*' is out of date commit error.

I have the latest version checked out (so far as I can tell). svn st -u turns up no differences other than the mv commands.

I sometimes get this with TortoiseSVN on windows. The solution for me is to svn update the directory, even though there are no revisions to download or update. It does something to the metadata, which magically fixes it.