I'm trying to use Data Loader to import a group of opportunities. Everytime I run the Data Loader it only imports the first record. All the other records fail with the message "An unexpected error occurred during the import of the following row: 'External Unique Id: xxxxxxx'". After running the Data Loader, I can modify the Data file and remove the first record that was imported. By running the Data Loader again, the first row (previously the second row) will import successfully.