Drools Sample.drl is broken

Hello, I use drools plugin (6.4.0.Final) in Eclipse Neon. I followed the wizard to create a drools project with some example files. After the step were done, Eclipse highlighted errors at the two rules in the Sample.drl file. Here is one of the errors:

Multiple markers at this line

• com.sample.DroolsTest.Message cannot be resolved to a type
• org.drools.core.util.bitmask.AllSetBitMask cannot be resolved to a type
• Only a type can be imported. com.sample.DroolsTest.Message resolves to a package
• org.kie.api.runtime.rule.FactHandle cannot be resolved to a type
• KnowledgeHelper cannot be resolved to a type
• Only a type can be imported. org.drools.core.spi.KnowledgeHelper resolves to a package
• Message.GOODBYE cannot be resolved to a type
• org.kie.api.runtime.rule.RuleContext cannot be resolved to a type
• java.lang.Exception cannot be resolved to a type

When I ran DroolsTest.java, I got the following error:
java.lang.RuntimeException: Error while creating KieBase[Message [id=1, level=ERROR, path=Sample.drl, line=15, column=0
text=Rule Compilation error Only a type can be imported. com.sample.DroolsTest.Message resolves to a package
Only a type can be imported. org.drools.core.spi.KnowledgeHelper resolves to a package
KnowledgeHelper cannot be resolved to a type
org.kie.api.runtime.rule.FactHandle cannot be resolved to a type
java.lang.Exception cannot be resolved to a type
org.kie.api.runtime.rule.RuleContext cannot be resolved to a type], Message [id=2, level=ERROR, path=Sample.drl, line=5, column=0
text=Rule Compilation error Only a type can be imported. com.sample.DroolsTest.Message resolves to a package
Only a type can be imported. org.drools.core.spi.KnowledgeHelper resolves to a package
KnowledgeHelper cannot be resolved to a type
com.sample.DroolsTest.Message cannot be resolved to a type
org.kie.api.runtime.rule.FactHandle cannot be resolved to a type
org.kie.api.runtime.rule.FactHandle cannot be resolved to a type
java.lang.Exception cannot be resolved to a type
org.kie.api.runtime.rule.RuleContext cannot be resolved to a type
Message.GOODBYE cannot be resolved to a type
org.drools.core.util.bitmask.AllSetBitMask cannot be resolved to a type
com.sample.DroolsTest.Message cannot be resolved to a type]]
at org.drools.compiler.kie.builder.impl.KieContainerImpl.getKieBase(KieContainerImpl.java:450)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:604)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:575)

It seems like an library path issue. Please help!

Thank you very much!

Tianwei Chen