I have found the solution:
1, go to the server
2, copy the Repositories folder from C: to D:
3, launch the VisualSVN Server Manager
4, right click VisualSVN Server(Local), select Properties
5, add the new path, uncheck the permission checkbox
6, hit OK
If you find a problem (error message) then check the permissions of the folder on the C: drive and compare it to the folder on the D: drive. Make them the same and you are ready to go!
------------------------------------------------------
http://tortoisesvn.tigris.org/ds/viewMessage.do?dsForumId=4061&dsMessageId=2592682