I've tried copying the specific slice that gives the error, and that is the one which gives the -36 error. I've seen the online advice claiming that this error is somehow to do with . files on FAT partitions, but that isn't the case here, and I can't find anything online which talks about that error in any other context. I tried dot_clean, but it didn't help.
My guess would be that the slice file itself is corrupted somehow. I am also finding that Mac OS has been running slowly, for the last week or so, but haven't been able to get into its Diagnostics mode to find out what the problem is. Disk Repair reports that the disk concerned is fine, and has no problems. The virtual disk for the VM is on the same drive as my Mac OS boot partition, which is a 1TB SSD.