Custom Language Support - newbie issue...

I have a simple grammar mimicking from http://www.jetbrains.org/intellij/sdk/docs/tutorials/custom_language_support/grammar_and_parser.html 

The grammar file is

{
 parserClass = "com.home.parser.RulesParser"

 extends = "com.intellij.extapi.psi.ASTWrapperPsiElement"

 psiClassPrefix = "Rule"
 psiImplClassSuffix = "Impl"
 psiPackage = "com.home.plugin.psi"
 psiImplPackage = "com.home.plugin.psi.impl"

 elementTypeHolderClass = "com.home.plugin.psi.RulesTypes"
 elementTypeClass = "com.home.plugin.RuleElementType"
 tokenTypeClass = "com.home.plugin.RuleTokenType"

 psiImplUtilClass = "com.home.plugin.psi.impl.RulePsiImplUtil"

 tokens = [
 INCLUDE_FILE = '*include-file*'
 space = 'regexp:\s+'
 comment = 'regexp:[#|//].*'
 string = "regexp:\"[^\"]*\"|'[^']*'"

 ]
}

ruleFile ::= spacing sections

sections ::= [ spacing include-section spacing ]

include-section ::= (INCLUDE_FILE space+ string)*

spacing ::= (space | comment)*

when i generate parser code, the RuleTypes java generated has compile error:

Error:(19, 16) java: variable INCLUDE_SECTION is already defined in interface com.home.plugin.psi.RulesTypes

This is my first attempt to work on plugins. I tried searching for info regarding this subject and have been unsuccessful. Any help appreciated.