This error occured to me and took me a while to fix, the most fun part is that when you try and google this error (at the time of this writing) there is no result that actually solves the problem - furthermore, there are only about 5 hits that are unrelated to the actual error.
Though I'm not sure how often the error occurs, it happens when you have two dependencies in your pom.xml file (assuming you are using maven, otherwise it's two libraries that conflict).
If you delete the following entry
<dependency> <groupId>org.glassfish.main.appclient</groupId> <artifactId>gf-client</artifactId> <version>4.0</version> </dependency>
It should fix the problem. (and if you set up your plugins correctly, glassfish will still work.)