Hi Gimmely,
ok - the VMs themselves are on USB external drives
my C: drive is a small SSD, so complely not enough space to copy the VM on to!
I could not find any obvious log files for the VM workstation installation itself (do you happen to know where they get put &/or the naming convention?)
I found a log file on one of the VM drive - I have attached it here
I tried creating a fresh very small un-OS-populated VM on the C drive & then creating snapshots on that VM - that worked ... but it did not reset anything centrally that the othe VMs needed reset to allow working with their snapshots, unfortunately!