Mike, I narrowed the issue down to improper syntax when changing to a directory or mounting a d64 image using the load syntax. If you don’t include $: in the load command for a directory then the machine will usually crash. Also attempting to mount a .d64 without including the .d64 extension in the file name will also cause problems.
Thought I should clarify my earlier comment about corrupted director. Thanks for a great bit of kit!
Mike