"Attempted to lock an already-locked dir" using SVNANT

Question

I'm using SVNANT for checking out my project directory on my Windows XP machine. The first time I've used tortoiseSVN for the check out.. as result I obtained an error message relative to the incompatible versions so I had to fix it using a downgrade script. Now,I can't use tortoiseSVN for any operation on my project folder because of this uncompatibility issue. The problem is that everytime I try to check out the project with SVNANT I receive this message:

Attempted to lock an already-locked dir

to be fixed this problem require a

svn cleanup

but as told above I cannot use Tortoise. How could I fix the problem?

thanks