Error "An error has occurred in <workflow name>" in Workflow That Fails to Create Task but Sends Response No Longer Required Email
When running a workflow that creates a task, the workflow fails and sends an email indicating that a response no longer required. Additionally, the workflow history shows the following error:
An error has occurred in <workflow name>
When viewing the task list after running the workflow, no task was created by the workflow.
Ensure the list settings of the Task List used by the workflow are not set to enforce unique values.
This issue is the result of one column being set to enforce unique values--generally the title field. The workflow fails to create the task due to the unique value constraint on the task list. If a new task list is created and the same error occurs, it is likely that the "Title" site column has been altered to enforce unique values.