I'm running VMware Workstation Player 15 on a Win7 host. I'm trying to use an Ubuntu 16.04LTS client to do partitioning, cloning, and other related things on disks. I was able to create a bunch of partitions on a blank SSD, and they're visible both in Windows Disk Management, and under Linux in the /dev tree. When I try to use the dd command to try to copy an existing partition on an old drive over the empty partition on the new drive, which has the same size, I can't write to it at all, because I get popups from the VM with the message mentioned in the title. Neither drive is mounted in Linux. I've tried it with the drives online and offline in Windows, and it makes no difference.
I can do this stuff by just booting direct to Linux (meaning there's nothing wrong with the disks), but I need to go back and forth between Linux and Windows tools, and repeatedly rebooting makes my work really difficult.
So what does this error message mean, what causes it, and what do I do about it?