I am getting an error like this:
[WARN]Warning: Multiple build commands for output file /Developer/B/Be/build/Release-iphonesimulator/BB.app/no.png
[WARN]Warning: Multiple build commands for output file /Developer/B/Be/build/Release-iphonesimulator/BB.app/d.png
[WARN]Warning: Multiple build commands for output file /Developer/B/Be/build/Release-iphonesimulator/BB.app/n.png
But I have checked Xcode and I don't see any duplicates of such files at all. As this post in the Apple Mailing Lists say, there are no duplicates.
In the Project Navigator, select your Xcode Project file. This will show you the project settings as well as the targets in the project. Look in the "Copy Bundle Resources" Build Phase. You should find the offending files in that list twice. Delete the duplicate reference.
Xcode is complaining that you are trying to bundle the same file with your application two times.