Our tablets are unable to update to the latest version of our application. it keeps throwing us an error for every tablet that we try to update: APK installation failed: [INSTALL_FAILED_VERIFICATION_FAILURE]

I have tried a few different methods. It has only been delivered successfully to 1 tablet. from all the other tablets i have tried it has failed with that error. I did a quick google, and it says to make sure that you allow apps unknown sources/apps to be installed which is set on all the tablets.

I have tried to delete the data/cache and then install, still failed. I even delete manually the program from the device and it still fails.

I need a answer to this issue asap as it is blocking us from pushing this to all our tablets.

Thanks.