Hi Martin,
can you post the Execption and stacktrace or the exact error message you encounter?
The Bad Major Version usually indicates that the JVM you use to execute the bytecode is older than the version you used to compile it. You can try to set the compiler compliance level to e.g. 1.6 to force compatibility with older JVMs. This settings is available in Windows > Preferences > Java > Compiler.
Source: Re: “Bad Major Version” Error