Coherent mode does not show windows on desktop

I have latest Paralles 8 installed on latest Mountain Lion

I'm using Windows XP SP3.

I have 4 Mac users each with a different Parallels instance.

One user - the one that installed Parallels 8 - displays Windows coherently. All the others do not. That is, in coherent mode the window is not seen. If I Exit coherence I can see the window in the Windows Desktop.

I have upgraded the Parallels tools in each instance.

I have restarted each instance from within Windows.

Can anyone shed light on This?

warm regards