When we are trying to import a project configuration file (XML), during the simulation step this error is showed "Unmet pre-condition: Custom field must exist".  This custom fields are referenced in validators and conditions generated by Workflow Toolbox plugin. 

Expected Behaviour

This custom fields must be properly treated on import process. 

Workaround

• Eliminate validators and conditions from source instance
• Generate the xml file
• Run import process
• create validator and conditions manually in target instance.