Steps to simulate:

• Create a dummy Perforce template job (I called mine 'template_test')

  p4 client template_test

• Create a Jenkins job: (I called mine 'TestJob' – Freestyle project)
  • Source Code Management = Perforce Software
    • Workspace behaviour: Template (view generated from node)
    • Workspace Name Format: Test-${NODE_NAME}-${JOB_NAME}
• Build newly created job (it should be green since it doesnt do much)
• Delete the perforce template

  p4 client -d template_test

• Try and delete the previously created Jenkins Project (i.e. click on 'Delete Project') and it crashes with this error:
  • Jenkins 1.642.4 – Perforce plugin ver 1.4.14
    
  • Jenkins 2.121.3 – Perforce plugin ver 1.10.6
    

Manually deleting all the previous run jobs and then deleting the project works