Can't delete files from a MyBook World

I have windows 7 64bit.
I bought WESTERN DIGITAL My Book World Edition II 2TB with ethernet drive.
it was working well for 3 years but now it is not working

but I can explore all files ok but can’t delete any folder\files on My Book World drive.

error permission denied

can anybody knows what problem is?

Are you log in on the drive as the administrator?