To fix this issue do the following:|
Settings Installed Apps
To top right corner tap on this window click the SETTINGS icon (3 vertical dots)
Click Show All Apps
Now Scroll Down and Search for "File Manager"
It should be ENABLED (if not then tap on Disabled and Toggle to ENABLE it)
Now tap on Clear Data and Clear All Data
REBOOT the phone (This step is necessary to solve this issue)
After Reboot again go back into Installed Apps and search for
"com.android.fileexplorer.FileExplorer..." Tap on it
AUTOSTART must be Enabled
Now Tap Permissions -- Enable all Permissions
After Reboot try moving some files from Internal Storage to SD Card it should be solved.
If not then try both the above steps once again.