Titanium Backup "insufficient free storage space" error Because of my external SD card issue, I thought I should factory reset my phone then reinstall the firmware on it. Before I'd do that though, I'd have to back up my apps and their data so that I can restore it afterwards. For that purpose, I had been relying on Titanium Backup Pro, so I entered the app, changed the backup directory to /storage/emulated/legacy/TitaniumBackup (as the external SD card was unavailable) and attempted to backup all user apps and system data. A progress dialogue appeared and was stuck at 0% for about 30 seconds until it close and Titanium Backup displayed the notification 'Batch backup interrupted: Insufficient free storage space' despite having 7 gigabytes left on /storage/emulated/legacy.

I tried searching on Google for a solution - the only one that came up was to remove /data/app/com.keramidas.TitaniumBackup-1.odex but the file did not exist on my end. How can I fix this issue?

Clarification: My copy of Titanium Backup is a Pro version activated by a Pro key obtained from the Google Play store. There is no need for any external patchers, cracks or keygens.
This is due to the 'Mount namespace separation' setting in SuperSU being turned on (by default). Untick that, reboot and try your Titanium Backup operation again.

This happens because the permissions to app-created folders are restricted in newer Android versions, I believe. Ironically, I didn't have this issue on Marshmallow-based CM13, but I did face it in the Lollipop-based OxygenOS for the OnePlus One.