Cannot access variable "manager" in Jenkins

I am trying to run a Groovy script as a post build action. Unfortunately I cannot use the variable manager

. The following code:

import jenkins.*
import jenkins.model.*
import hudson.*
import hudson.model.*
def failedSummary = manager.createSummary('error.gif')

      

        
        
        
      

    

raises this error:

groovy.lang.MissingPropertyException: No such property: manager for class: Script1

Please, help.