Just ran into the same problem. I had to interrupt a checkout because it was taking an absurdly long time. When I went to “resume” the checkout, it wasn’t clear whether I should re-initiate the checkout or simply do an svn update.
After attempting to to do the svn update to resume the checkout, I got a wonderful error message saying that the directory was “locked”. I tried issuing a “Release Lock” from Tortoise SVN, but this didn’t help.
Ultimately, what I ended up having to do was issue an svn cleanup to release whatever stranglehold Subversion had in place. After that, I was able to continue my previously initiated checkout by performing kicking off another update (svn update or “SVN Update” from the Tortoise SVN context menu).