The problem is the independent (non-persistent or persistent) disk. While using an independent (non-persistent or persistent) disk, you are not allowed to take snapshots of a powered on machine.
You can for example, change the drive to non-independent (default) mode, which will allow you to take snapshots, while powered on. This will allow you to take snapshots.
- Power off the virtual machine.
- Delete existing snapshots.
- Select the virtual machine and select VM > Settings.
- On the Hardware tab, select the drive to include and click Advanced.
- Unchek Independent.
Why does VMWare prevent you from
This could be explained because of the behaviour of non-persistent drives: "Changes to the disk are discarded when you power off or revert to that snapshot."
So as it discards any changes on powering on, you would loose changes, which are saved to a snapshot.
Information found here:
PDF - Using VMWW 8.X