Can't Move to External SD Card

I was unable to move some big apps that usually have .obb files in it... It's happened recently after I did factory reset my phone... also when trying to download some app, if i set my external storage as my main download storage, I'm getting some kind of error 963...  My External SD Card still got a lot of space and I still able to access my SD Card.... please help! It never happened before...

try below :

1) Clear Apps Cache:

Go to Settings > Apps > All
Select Play Store > Clear Cache & Data.
Select the app that was showing the error and Clear cache and data. Now try and download the app again and see if the error still persists. If the Caches were the problem, your issue must be solved

2) Unmount SD Card:

Go to Settings > Storage > Unmount SD Card. Now try and download or update the app . Once you successfully Download the app without any error, Now its time to Re-Mount SD Card by Navigating to Settings > Storage > Re-mount SD Card.

If the app which is giving you error is in SD Card then you should first try to move it to Internal storage. To do so, Go to Settings > Apps > All > Select the App > Move to Internal storage.