I found this thread after google searching the error code after I experienced it with my unlocked/rooted Nexus 5. After some fiddling, I found a solution that worked for me. Unfortunately to those without it, it requires the use of an app that needs root. My unlocked Nexus 5 is on the stock ROM/kernel, and no other big changes have been made to /system besides rooting (no xposed or anything else).
Without further ado, my silver bullet solution is an app by darken called SD Maid.
Play Store link Download and install it, and carefully heed the warning it gives you that it is a powerful root app. Then, what you want to do is run the "CorpseFinder" function. As the Play Store listing explains, the feature "searches your device for orphaned items and compares those to the list of installed applications." The idea is that many times, uninstalling apps out there a ton of junk on our devices, and the purpose of this app is to find those and give you the option to remove them. Tap the trash can to delete the corpses, then reboot your phone and try to install the apps you had trouble with again. It worked for me, please report back if this works for you.
A little context: I started getting the 960 error after flashing KTU84P (android 4.4.4) to my Nexus 5 from the bootloader over ADB. I tried to download some apps I had installed previously, and those were the only apps I got the error with. Alarmingly, when I googled searched code 960, it seemed for some folks that the error survived factory resets!
See this thread.
This didn't make a lot of sense to me, because even if the error survived a stock factory reset that wipes /data, flashing the full nexus image, as far as I knew, would do a full wipe of everything before restoring the nexus image to its respective partitions (system, data, etc). I did swap out the stock recovery for TWRP before flashing it, but I can't remember more details about what I did. Nevertheless, after I started getting the 960 error with other apps, I went ahead and downloaded SD Maid because I usually have it installed on my phone anyway (it's a great app that can clear out a ton of space). There shouldn't BE corpses on internal memory after a fresh install. Regardless, I ran CorpseFinder, removed what it found, rebooted the phone, and I ceased to have any issues. Keep in mind that the app wasn't developed to address this error, specifically, so if it doesn't work for you, don't blame the dev. If it works for you, considering
buying the Pro key 
If you do try this method and find corpses, it might be helpful to make a note of them and post them here so further debugging can be done. I wish I would have thought of that before having the app remove the corpses it found.
edit: wow, my sig here is in sore need of updating.
