Often times, you can get an "insufficient storage" error, caused by duplicate folders in /data/app-lib. Deleting the oldest of the folders fixes the problem.
However, since this app needs to access and delete folders in /data/app-lib, it requires you to be rooted.
Extra info for those who still have issues:
On some phones and configurations (specifically Android versions <4.1), the app will crash. I am aware of this issue and am working to fix it.
In the meantime, if the insufficient storage error is a problem for you, you can manually fix the problem through a (root-enabled) file browser: Just navigate to /data/app-lib, then delete all of the lowest-numbered duplicate folders inside.
For example, if you had something like "com.zikaeroh.insufixer-1" and "com.zikaeroh.insufixer-2", then you would delete the first of the two, leaving the highest number only.
Remember, I am not responsible for lost data.
It lists the storage areas available on your device including internal storage, SD cards and attached devices such as hard drives, showing the total and used space on each. You can then scan each one and view them in detail, and delete files which are no longer needed.
Storage analyzer is free, with no popup or full screen ads, and is easy to use.