currently I'm trying to import approx 1600 tasks from Azure DevOps Kanban board to another one (via browser). I've faced two problems by doing this:
- It is not possible to import the task with Closed Date field, it says:
Value of a readonly field Closed Date was modified. Please revert the Closed Date values or remove the column from the input file and and try to import again.
- Removing the column with "Closed Date" will cause issue with default state "Done", it says:
The field 'State' contains the value 'Done' that is not in the list of supported values.
I've copied (manually) the project settings from old Organization to new, such as:
Also, I had to remove the ID column, because it caused the issue:

Still it is not possible to import all these tasks because of the issues. I'm looking for any tips how to fix this. Below there's an example of CSV:
Work Item Type,Title,Created By,Created Date,Assigned To,State
Issue,Some test task number 1,TestCreator,02.06.2020 15:19:24,TestWorker,"Done"
Issue,Some test task number 2,TestCreator,02.06.2020 15:20:23,TestWorker,"Done"




When importing work items via CSV file in Azure DevOps, first make the following statements are true:
1.The source project to export and target project to import has the same work item type configuration, in common, they need to have the same process configuration, for example, work item type, state.
2.All work items you import are created in a new state. This rule means that you can't specify field values that don't meet the field rules for the new state. (That's why "Done" that is not listed as supported value)
3.Make sure you don't assign IDs to new work items that you're adding. Work item ID is unique in one Azure DevOps organization. (ID will cause the following error message)
With the above prerequisites, the import process loads the imported work items into the queries view in an unsaved state. No IDs are assigned. Verify the results are what you want. Then, choose Save Items to save the work items.
If you still get the error when importing, try reduce the work item counts for per import attempt. As you said, you have approx 1600 tasks, you could import by separating them into several queries.