SOLUTION 1:
Are you using proguard? if so.. you might want to replace the one in the sdk (C:\android-sdk\tools2\proguard*) with the latest version from here.
You can rename the old proguard to proguard2 and place the downloaded version in C:\android-sdk\tools2\proguard*
*Note: the folder of your AndroidSDK might be different
SOLUTION 2:
If you had imported other projects as libraries for the main project you might check if those libraries are imported twice:

Those Images were extracted from this answer
SOLUTION 3:
Create a new Android project with the same package name, copy all your resources, Manifest and source files, configure the external libraries and then try to compile the new project