After installing OS 10.11.5 few days ago, my Mac freeze going in "power save mode".
I thought it could be related to BOINC, so I stopped it and removed it as my screensaver, and now this problem has disappeared...
Is it a problem of my Mac, or could be a problem between BOINC and OS 10.11.5?
Am I the only Mac owner experimenting this issue?

After other tests, I've come to the conclusion that the problem doesn't lie in BOINC itself, but in its screensaver; so, as far I'm concerned, the problem is "solved": I want BOINC running, I don't care of its screensaver!

Although I don't have 10.11 on my iMac, I know there are problems with certain projects and the screensaver--such as Einstein.