ralfb1, It seems a hidden snapshot somehow. So, you need to delete it manually by using Terminal commands. There is an example:
Important Note: Make sure you have 200GB of free space (in your case) at least on your Mac to successful deleting the snapshot.
1. Shutdown you VM.
2. Launch Terminal.app (/Applications/Utilities folder)
3. List all your registered VMs by prlctl list -a command. I have marked by red color the target VM.
4. Copy its ID and execute the prlctl snapshot-list command
5. Delete the snapshot by using prlctl snapshot-delete command and use ID of VM (in red) and ID of Snapshot (in blue)
alexanders-mbp:vm alexg$ prlctl list -a
UUID STATUS IP_ADDR NAME
{15f76d21-b4b5-4807-857d-826c69b8fc9d} suspended - Windows 10 1703
{f86a10cc-9fdb-4568-ba9c-528e30197f30} stopped - Windows 2000 SP4 x32 UP
alexanders-mbp:vm alexg$ prlctl snapshot-list {f86a10cc-9fdb-4568-ba9c-528e30197f30}
PARENT_SNAPSHOT_ID SNAPSHOT_ID
*{98934153-051b-41c4-a57d-cf9e83fed378}
alexanders-mbp:vm alexg$ prlctl snapshot-delete {f86a10cc-9fdb-4568-ba9c-528e30197f30} -i {98934153-051b-41c4-a57d-cf9e83fed378}
Delete the snapshot...
The snapshot has been successfully deleted.
alexanders-mbp:vm alexg$
Last edited: Dec 28, 2017