Error compiling Groovy "Build Engines" Script

I've been testing the 'build engines' script with RTC Build Toolkit 4.05, and 5.02 using Groovy 1.8.9, and unfortunately I get the following errors:

7 compilation errors:
	
	
	

unable to resolve class com.ibm.team.build.common.model.query.IBaseBuildResultQueryModel.IBuildResultQueryModel
	
	
	

 at line: 19, column: 1
	
	
	

unable to resolve class com.ibm.team.build.common.model.query.IBaseBuildEngineQueryModel.IBuildEngineQueryModel
	
	
	

 at line: 20, column: 1
	
	
	

unable to resolve class IItemQueryPage 
	
	
	

 at line: 80, column: 28
	
	
	

unable to resolve class ILoginHandler2 
	
	
	

 at line: 34, column: 5
	
	
	

unable to resolve class ITeamRepository 
	
	
	

 at line: 37, column: 35
	
	
	

unable to resolve class ILoginInfo2 
	
	
	

 at line: 37, column: 9
	
	
	

unable to resolve class UsernameAndPasswordLoginInfo 
	
	
	

 at line: 39, column: 13
	
	
	

The Build Toolkit jars are in the Groovy classpath, but obviously, dependencies that cause the errors are not there.

Question: is there something I missed, or am I using the wrong version of the BTK? Which would be the right version?