Ahhh.....I was afraid they might charge you to upgrade.
Thats how they get you.
If you want to use all the latest OS's (win10) and the latest software OSX (Mac OSX El Cap), then they force you to ALSO have the latest Paralels software too.
Keeping everything up to date, is th eonly sure way to know we can get things working properly.
Newer version have the necessary patches that the previous version had problems with.
Especially when the OS is new (Win10.
You ahve 3 interdepenceies at work here.
Your Mac OSX
All have to work together to get what you need.
These are HUGE pieces of software with millions of lines of code. Can be challenging.
But if your up to date.....it makes it mUCH easier to pin down the actual problem, and then you can report it if there is no fix, so THEY (paralels or Mac, or Microsoft) can address and relase a patch or update.