I had windows running in bootcamp that worked well with Yosemite and Parallels 10 (when upgraded from 9 early Nov), when things were all working as usual, i upgraded to El and parallels complained about not able to find some drive /users... when i googled about that problem, the solution was to upgrade to Parallels 11.
I have now downgraded to Yosemite and installed Parallels with a Window 7 enterprise image (not bootcamp this time). I am now scared of upgrading to El Cap.