Due to Fat32 File System Format of some files in your device you may be unable to change the permission of the files with Root Explorer.
A quick fix of this error is to –
- Open Root Explorer File Manager.
- Navigate to /Data/Media/0/
- Search your file -> Long press it -> Change File Permission.
The files in data/media/0/ are in Ext3/Ext4 format which is why you can easily change the permission.