Booting VM from external HDD on multiple machines

I used to have my VM on a portable USB drive. I boot it on my MacBook Pro with no problems. I used to be able to boot it on my Mac Pro too.

Recently I can only boot it on the MBP. When I shut it down and try to boot on the Mac Pro (after moving the external usb cable to the Mac Pro), it tries to register the VM but after telling it I moved the VM, it complains that it could not locate the VM files. So I point it to the .pvm package on the portable HDD, then the same error keeps showing up.

Why could I previously move the VM between machines with no problems, but now it refuses to run on the Mac Pro and only runs on the MBP? It seems like the last one or two builds did this...

 

It is permissions issue,
try to repair permissions on external HDD

 

Does not make difference. I fixed permissions and no errors were found (on external drive). I then fixed permissions on my internal drive - also no difference. I unticked "Ignore owner" on the external drive - no difference. I get:

"The virtual machine is corrupted.

The virtual machine cannot be used because its files are corrupted."

But it boots on my other machine??