Android : android studio resourcebundle missingresourceexception

I'm trying to migrate from eclipse to Android studio. After some work I got my app to build but I get a missingresourcefileexception.

I have my achievements.properties file in the src folder of my app. Which runs fine when I build and run in eclipse.

In android studio however I get the following exception:

04-14 21:02:09.657  16105-16152/com.bla E/AndroidRuntime﹕ FATAL EXCEPTION: GLThread 37579
Process: com.streefgames.rotatris.android, PID: 16105
java.util.MissingResourceException: Can't find resource for bundle 'achievements_en', key ''
        at java.util.ResourceBundle.missingResourceException(ResourceBundle.java:238)
        at java.util.ResourceBundle.getBundle(ResourceBundle.java:230)
        at java.util.ResourceBundle.getBundle(ResourceBundle.java:159)
        at com.streefgames.rotatris.helpers.StringResourceManager.<init>(StringResourceManager.java:18)

I have tried moving my resource file around, adding resource files to make a bundle, different locales and all the other things I found. But it is still not working. Any idea what's wrong?