Import Error due to Workflow
When you import a document of a DocType which has a workflow, you shouldn't be able to set the workflow_state to a state except the first.
For example, your Workflow has 4 states: Draft, Sent for Approval, Approved, Rejected.
You prepare records to import using Data Import Tool, and you set the workflow_state of each record to Approved. The system will not allow this, because you are transitioning from the state Draft to Approved which is not a valid transition according to your workflow.
The solution is to disable the workflow, import your data and then enable the workflow again.