Managed to resolve this myself.
As suspected - the error message relating to registry access and resources was misleading.
The problem was permissions to the shared directories. We had set a single directory on the host to contain all the shared data for for all guests, and then enabled individual directories within the share so that each guest OS could only see its own data.
The problem appeared to be that because there were two directories in the underlying UNC path that each guest OS didn't have permissions to read or write to, the guest machines were crashing - even though the user running the VMWare process on the host had full permissions to the entire path.
The resolution came to light when I attempted to set robocopy to mirror the guests data onto the host - the command came back with pernmission denied. Mapping the root of the shared area has resolved the problem - but of course this now means that each guest can browse to the others shared data. We will resolve this issue by another method.