High CPU with VMware Fusion and 2 VMs

Here is a strange one - 

I'm running Norton 360 on a Win7x64 VM on a MacBook Pro under VMWare fusion. All is fine.

But if I start a second VM on the same host machine, even though that is not running Norton 360 (just a bare bones Win7 VM) - the copy of N360 on the first VM starts to eat up all the CPU (up to 100%) when I do anything e.g. edit a Word document. I can only stop it by closing the second VM and rebooting the first one.

Just to be clear, doing exactly the same activities when the second VM is not running, and I don't get any issues with N360.

And it is only the N360 service that displays this behaviour.

Since each VM should be separate, and I have plenty of resources, I can't think why having the other VM running should affect N360 - but it happens consistently without fail.

I just don't know where to start looking ..

 

Any ideas?

Thanks!