You can't use any apps like this any more. Because lots of apps abused the MEDIA_MOUNTED broadcast intent to cause a rescan of the whole filesystem (draining battery) after they only changed one file, KitKat has a new restriction that only system apps can broadcast this intent. Apps that try will get a SecurityException, which by default causes the "... has stopped" dialog.
There's an alternative mechanism for an app to say that it's changed a particular file, and cause that file to be rescanned (not recursively), but (a) there's no replacement that scans a whole filesystem, because that would be abused in the same way; and (b) it's up to the app to call this. It's not something you can change as a user.
An app that used root would be able to make this work in the same way as 4.3 and earlier, but again, it would need to be specifically written to request root. Rooting the device wouldn't make your old apps start working again.
For more technical details, see How to trigger MediaScan on Nexus 7?How to trigger MediaScan on Nexus 7? on Stack Overflow, our sister site for programming questions.
