I had previously attempted to install an app but the device shut down mid installation. When I tried to install the app again at a later point in time the installation failed resulting in the Error -24 being shown on the play store.

So chances are you, as I did, are seeing an Error -24 message because remnants of a previous app installation remain.

Prerequisites to solving the problem:

To resolve this error install a file browser that will navigate to the system folders of the device, i.e. Root Browser. (Note: you’ll need root access to get to the necessary folder. You can view the following tutorial for an idea of what’s involved in rooting your device.)

Solution For An Error -24 :

STEP 1: In Root Browser tap the Data folder, then tap the Data folder again (One data folder is inside the other)

STEP 2: Find the remnant of the previous installation e.g. com.your.packagename and delete it. At this point you can try install the app again. If the installation fails repeat steps 1 & 2 and then move onto step 3.

Warning this next step is necessary but may have unwanted consequences as it involves wiping the cache of Google Play Services. The following paragraph is an over view of what google play services is and what it does. After reading the description you will be proceeding at your own risk.

Google Play services is used to update Google apps and apps from Google Play.
This component provides core functionality like authentication to your Google services, synchronized contacts, access to all the latest user privacy settings, and higher quality, lower-powered location based services.
Google Play services also enhances your app experience. It speeds up offline searches, provides more immersive maps, and improves gaming experiences.
Apps may not work if you uninstall Google Play services.

STEP 3: Go to Android Settings > Apps > swipe to All and scroll down to Google Play Services, tap on the app and then tap on clear cache button.

You should now be able to download and install that pesky app.