I cannot delete a folder

I have folder in my repository that somehow has a name with ':' in it. This is causing problems with a clients SVN software (Tortoise).

I have tried deleting it in my local copy but I get SVN errors saying it cannot find a URL. I have tried deleting it by connecting to the repository via webdav, but I get a conflict error. I'm new to SVN so any tips would be very helpful!