So I wanted to transfer some file in data transfer mode, but the phone kept saying that the mass memory was in use by another app.😡 So after forever of deleting apps and rebooting it ended up being the Full Screen Caller app that was causing all the problems. This really frustrated me, but at least I got rid of all my unnecessary apps. 😊
Solved my "Mass Memory In Use" problem
Another one to watch out for is if you use Mass Memory for your texts.