Xcopy cannot create directory

My backup cmd file has been in use since XP, through Vista to Win7. It has worked on a new laptop in Win7 ever since Win7 was released. Recently it has stopped working getting an access denied, cannot create directory message. It is xcopying my own folders, not the default documents etc.
In a cmd prompt, xcopy d:\data z:\ fails with the error, but copy d:\data z:\ doesn't.
Has MS patched xcopy recently? If so, how can I get back the earlier version?

Hi Golden

Using exactly as you suggest gives error "Access denied".

The strange thing I find is COPY works but XCOPY doesn't!

Cheers

Dougham

Has your Z drive always been connected to your Win7 machine or have you recently connected your external Z drive to another machine?

The Z: drive is a network drive, not connected specifically to the Win7. My desktop and my wife's laptop all have a drive mapped to the NAS.
Again I come back to why copy works but not xcopy.

And nothing has changed in your batch file between the times it worked and now that it doesn't?

I would verify you still have the proper permissions on the drive in the NAS as well.

No the batch file hasn't changed.
I am doing all the tests manually now

I've attached the output from another attempt. I copy OK, but can't xcopy.