can not delete folder because lock

[netvampire.tw]

Dear
    I use Subversion 1.6.13 recently, we want to delete a folder but fail.The 
error message said there is a file name xxxx is locked by someone. try to 
release lock or steal lock.
But the file already didn't exist. So we can not lock it. what happened to us?
How could we do? thanks.~
Best regards,
EdwinTai