The cause:
This generic message only appears alongside a different (specific error) when trying to export from Pleo to Datev. Because of a specific error, all other expenses in the same batch fail to be exported.
The solution:
Find the error message that's accompanied by the text "weitere Daten dieser Verarbeitung können nicht übernommen werden” (English: cannot process this data further).
Click on “View Expense” so you know which Pleo expense is the culprit.
Type the error message into Pleo's help centre to find the solution.