You may have insufficient disk space! I had the same problem running virtualization on my mac. ( I had a fairly large collection of movies and music that unfortunately had to be weeded through to get the space for the virtual box.) What you need to do is clear the space, as the installation of parallels is like having another computer using all your hard drive space. If your virtual box gets a windows virus that eats up hard drive space, you may be susceptible to it even being on the mac, so second causes/solutions would be run malwarebytes and ccleaner to eliminate that possibility (inside the windows box of course). You can run them outside it as well, as cleaner has a mac version, and that will clean up the mac-side temp files.
www.malwarebytes.org <<malwarebytes free
www.piriform.com/ccleaner <<ccleaner free
It is going to be a memory issue, I just deleted 50gig worth of old movies I don't watch anymore and done deal.