Adding spock to eclipse without maven: General error during semantic analysis

I am trying to do my first test-automations with spock. I do not want to use maven. I am using eclipse java EE oxygen 4.7. I have created a groovy project. I have added the spock jar as external library in the build path configuration. Spock ist spock-core-1.1-groovy-2.4. I have also added geb jar the same way. However I am getting this strange error from automatic build, which I do not understand and I am seeking for help. So far I haven't found anything helpfull.

General error during semantic analysis: Transform org.spockframework.compiler.SpockTransform@xxxx cannot be run org.codehaus.groovy.GroovyException: Transform org.spockframework.compiler.SpockTransform@xxxx cannot be run at org.codehaus.groovy.transform.ASTTransformationVisitor$3.call(ASTTransformationVisitor.java:416) at org.codehaus.groovy.control.CompilationUnit.applyToSourceUnits(CompilationUnit.java:972) at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:633) at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:609) at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:586) at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.processToPhase(GroovyCompilationUnitDeclaration.java:217) at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.resolve(GroovyCompilationUnitDeclaration.java:613) at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:879) at org.eclipse.jdt.internal.compiler.ProcessTaskManager.run(ProcessTaskManager.java:141) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.NoClassDefFoundError: Unable to load class org.spockframework.runtime.ErrorCollector due to missing dependency org/junit/runners/model/MultipleFailureException at org.codehaus.groovy.vmplugin.v5.Java5.configureClassNode(Java5.java:397) at org.codehaus.groovy.ast.ClassNode.lazyClassInit(ClassNode.java:353) at org.codehaus.groovy.ast.ClassNode.getDeclaredMethods(ClassNode.java:981) at org.codehaus.groovy.ast.ImmutableClassNode.getDeclaredMethods(ImmutableClassNode.java:105) at org.spockframework.compiler.AstNodeCache.(AstNodeCache.java:65) at org.spockframework.compiler.SpockTransform$Impl.(SpockTransform.java: 52) at org.spockframework.compiler.SpockTransform.visit(SpockTransform.java:47) at org.codehaus.groovy.transform.ASTTransformationVisitor$3.call(ASTTransformationVisitor.java:395) ... 9 more

My code is as simple as you can get. This is the code:

//The error is on the "p" letter of package
package hellowworld 

class HelloWorld{

    static main(args) {
    }

}

Please note that this error only happens when I add spock jar. The closest question was Spock without maven or gradle, but obviousily the problems are different.