SFO Archive Forums - Installation problem

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Everytime i come to install certain programs it gives me a display message like this then says that installation failed prematurely, this is getting infuriating as i cant install some neccesary programs that i need..

Im not sure but the problem started when we installed our external hardrive ( outside computer HD ) but im not sure if this is the case; it says it has an invalid drive, but im pretty stumped as to what it means?

Could i please get some positive help from this.. thanks.