I am trying to distribute my application to some people for testing.
I have installed it on my Desire directly from eclipse and it works fine.

To create an APK-file, I choose *"Export Unsigned Application Package"* directly from eclipse, and then an APK file was created. I emailed it to myself and downloaded the file to the SD-card. But when I try to install it (using ES File Browser), I get a message saying *"Application not installed"*.

(I have already checked the "Allow installation of non-Market application" on my phone)
Any ideas?

**Yeah I found the problem, see my answer below:**

I did not know that even with the "[Allow Installation of non-Marked application](http://www.androiddevelopment.org/tag/apk/)", I still needed to sign the application.
I self-signed my application, following this link self-sign and release application, It only took 5 minutes, then I emailed the signed-APK file to myself and downloaded it to SD-card and then installed it without any problem.