I've not heard of anything like this happening before.  It sounds like when you attempt to mount Disk 1, that the action is being applied to Disk 2, instead of Disk 1 actually having a problem.  I'm guessing that this is happening when trying to mount the virtual disks from the PGP Desktop GUI.  If so, I'd suggest you go to the File menu and select Scan for PGP Disks.

I would also expect Disk 1 to mount correctly if you either double click on the pqd file for it, or right click on it and use the resulting PGP Desktop menu to mount it.

Just want to make sure that the problem isn't that mounting either one results in mounting to the same drive letter?  The mounting point can easily be changed if this is the problem - just click on the Options button before entering your passphrase for the mount.

Thanks for the comments

I tried changing all of the mount options including mounting it to T drive etc

When I try and access the data in T, I get access denied

To make it even more confusing, even though both disks that mount are 'Disk 2' instead of 1 and 2, the data isn't identical and some folders are missing

I also ran the scan for PGP disks and it found them both but it never actually fixed the issue