When the new Version 4 came out I purchased it with the understanding that it was better (wrong for me).
I ended up working for over a month with their (not so) technical support to no avail.
It would work the first time, and every time there after as long as I kept Fusion in the tray. When that was shut down, to free up memory, it wouldn't start the next time unless I rebooted.
Tech support gave me a number of things to try, and a couple of them 4 times for the same "fix".
I finally gave up and went back to Parallels which has been working just fine.
As mentioned, I purchased the upgrade for Fusion. When I asked for a refund they told me I should have downloaded the 30 day trial and that they wouldn't give me a refund.
So much for customer support.
Thanks for listening.