Here's how you fix Install Error 961
Method 1: Clearing the cache and data normally
1) To do this, go into your phone’s settings, then Applications (or Apps or Application Manager), swipe to the left to ”All” and scroll down until you find Google Play, tap on it.
2) In the app information page, tap on the button to empty the cache.
3) If this doesn’t solve the problem, try to delete the data from the Play Store which is found on the same page (Settings > Manage applications > Google Play > Delete data). This will most probably work, since it had worked in my case when I suffered with the problem in my android.
unknown install error 961
Method 2: Go to recovery mode and try again
If the above simple method doesn’t solve your problem, then a more thorough option is to do a system cache clear on your android device. Follow the following steps:
1) Power off your phone.
2) Hold volume up/down & power simultaneously until you see the Boot Mode Selection Menu
3) Use volume down to navigate to ‘Recovery’, use volume up to select. You should see screen with triangle and exclamation point next to an Android.
4) Press volume up/down simultaneously to go into system recovery.
5) Use volume rocker to navigate to ‘wipe cache’ and use power button to select
6) Once finished, use volume rocker to navigate to ‘reboot system now’ and use power button to select.