I'm taking a chance to post here, and I really hope someone would be able to assist me

It is my first android app.

I have created a very small android app. Basically it consists of a listview with two buttons:
The listview shows our courses. Once clicked, it shows the contents of each course
One button allows me to download a brochure
the other button opens up a form where the user can enter his / her details in order for us to be able to contact him / her

Nothing complicated.

Now I have debugged this app over and over to ensure everything will work fine.
On my AVD ( Samsung Galaxy SII ) everything works smoothly

So, I exported the release build with its signed key, and made it available for download from my website - not the google play store, as I want to gradually release it onto different platforms depending on the amount of downloads I get.

Right, so I download it and installed it on my phone ( Galaxy S II ) all 284 KB of it.
When I attempt to run it, my phone says that the app has stopped working and I must Force Close it.

What can it be?

I know this question seems vague, but perhaps there is a step I have missed.

Any guidance will be welcomed.