I have the same issue as referred to in http://stackoverflow.com/questions/9651703/using-proguard-with-android-without-obfuscation.
When the option -dontobfuscate is used in an Android project the export fails with "Conversion to Dalvik format failed with error 1".
I tried this with several projects and it's the same with all my projects. If I remove the option the build runs through without problems.
I'm using Eclipse 3.6.2, ADT 21.0.0 and ProGuard 4.8.
I attached a sample project based on the Snake sample included with the Android SDK to reproduce the problem.