Media scanning feature is broken in Android 4.4 Kitkat. Someone found out how to fix the bug. Link inside.

Wish they'd just add a permission instead of removing stuff all the time.

It's only the scan of the whole card that will not work anymore.

There is no 'fix' to apply.

The only workaround is for Tasker to recursively scan the whole card and
submit everything it finds for scanning, but that won't pick up deleted
files.

Will consider whether to just remove the 'whole card' option for KitKat+
or add the half-workaroun.

Pent

Was looking around as to why I couldn't get this to work and came across
trickster mods media scan function still working. It's detecting deleted
files, moved files, everything seems to work like it should. Not sure if
that info can help in any way, just thought I'd share.

I've made another attempt in the next update, let's wait and see.

Pent

Apparently system apps can still issue the rescan media card in kitkat, so
you could try converting Tasker to a system app (If you'r rooted)

RBX

I've tried the Media / Scan Card action both by leaving the "File"
parameter empty, putting "/" in there or putting "/storage/emulated/0" in
there ... neither seemed to work.

However from an ADB shell the following worked:
am broadcast -a android.intent.action.MEDIA_MOUNTED -d
file:///storage/emulated/0

So next I tried the Script / Run Shell action and used this as the
"command" parameter:
/system/bin/am broadcast -a android.intent.action.MEDIA_MOUNTED -d
file:///storage/emulated/0

Still didn't work, but the logcat error message pointed me in the right
direction:
W/ActivityManager( 488): Permission Denial: broadcast asks to run as user
-1 but is calling from user 0; this requires
android.permission.INTERACT_ACROSS_USERS_FULL or
android.permission.INTERACT_ACROSS_USERS

I've enabled the "Use Root" checkbox and it worked! Finally I've an action
that rescans the sdcard (I mean the /sdcard directory ... since it's not a
real SD card on my GNex)!

The "am" command can be even more specific ...
/system/bin/am broadcast -a android.intent.action.MEDIA_MOUNTED -n
com.android.providers.media/.MediaScannerReceiver -d
file:///storage/emulated/0

What it scans depends on what Android reports as 'the external storage' dir.

Pent