My problem I had was: com.Google.process.gapp has stopped and google play has stopped.
They would pop up every 2-3 seconds and my phone would refuse to sign in to google play at all. My phone a LG Sunrise has no boot mode for factory reset and it is straight talk and will not allow me to factory reset through settings. This was really annoying and made my phone unusable. After playing with setting I figured out this fix.
I had the same problem, and the download manager fix did not work.
What I did was....
Go to Settings>Apps>All
Find google play services
Disable and use device managed if prompted.
After disableing force stop the process.
Then uninstall ALL updates for google play services.
The sign into your google account through the play store.
Lastly go back to google play services on google play and update google play services.
I hope this works. Let me know if it did please.