First, I would suggest you to check the amount of free (available) disk space on your Mac hard disk. Right-click on the Mac HD > Get Info. This should show it. I suspect that there is very less amount of disk space on it and hence the error message.
If there is very less disk space available, then try to empty the trash (ensuring that you don't have anything important in it). Then delete the unnecessary files or move them onto an external hard disk. If you have movies, iMovie Projects, iTunes music etc, keeping them on an external hard disk should be a good idea.
Once you have freed up enough disk space (~ 2 to 4 GB), you should be able to start your virtual machine fine.