Lol @ "three minutes" *smile*. Alright, I found the time to uninstall and reinstall app world and this version is the one previously uninstalled (4.0.xxx). When I checked the app list the app that was giving trouble had "reinstall" as an option so I "reinstalled" it and it was installed successfully.
Re downgrading app world. I received a notification from app world that there was an upgrade for the programme. So, wanting to keep the programmes up to date, I followed instructions on the screen and downloaded the 'upgrade' only to discover that it asked me to uninstall 4.0 to install 3.xx. I don't know why, it just went that way.
Thank you for your help thus far (not sure if there is more). I've noticed several other persons posting a similar problem in the reviews for this app. Should I go ahead and ask them to try upgrading app world in some way?