Applications restore or install from external sd card I have Samsung Galaxy Duos Trans-S 7562. It had an problem with Wifi, so I sent the phone in for repairs. Before handing the phone over to store, I backed up the applications on the external Sd card.

Now applications can not be restored or installed. Only contacts are backed-up. The error message I get is Applications not downloaded from Google Play store can not be installed.

I used "Super backup-Contact And SMS" application for backing everything up.
This is due to the fact that by default non google-play applications are blocked by default in Android, as a security measure.
To allow these to be installed go to (this may vary in wording across Android Versions)
Settings &gt; Security &gt; Unknown Sources this allows things to be installed that are not form the known (Google Play Store) source.
You can, in later versions, set only the inital install to process or allow any further ones to install.
In android it is similar to this (slight variety in different versions)
http://www.fannsoftware.com/img/UnknownSrc.png
On the Kindle it is slightly different:

(source: bestvpn.com)