Upon opening VMware Workstation and attempting to power on any virtual machine I occasionally get the error below, stating "Internal Error."
The fix for this in my experience has been to start the VMware Workstation Server service. To view your services press the Windows Key + R (to open the Run prompt) then type services.msc and press Enter
As you can see, even though it is set to "Automatic", for whatever reason it doesn't always start automatically - usually after the computer has been restarted.
Simply right click the service and select "Start". Once the service is started you should be able to power on your VM's from VMware Workstation.