Problem with building apk file for android

Hello, please help !

Using eclipse I have tried to update the android sdk and then I stopped the update, and the build didnt work.

So I downloaded the latest sdk version and using unity i tried to build an apk file for android and it didnt work... the error said that i am missing an "aapt.exe" file and an "apkbuilder.bat" file. so I moved the "aapt.exe" and the "apkbuilder.bat" into the folders that unity was looking the files for and the build for the apk seemed like it was working. unity made an apk file for android but now every time I open the app in my android device the app crashes.

if someone knows what is the problem please help me it is very important

sorry if I had bad english... Thanks for everyone who helps