Unable to install my own application

I've developed android app, and via the eclipse debugging mode the apk install开发者_StackOverflow社区s and works successfully. but when I'm sending my unsigned APK to a friend, he gets after installation - Application Not Installed - without any error.

What can it be?

Thank you!

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You cannot install an unsigned APK. It can be signed by the debug signing key (what happens by default when you build) or signed with a production signing key, but it has to be signed.