Import Table Data is executed and in the last screen, "Specify Import Mode" screen, the "Save SQL statements to file" option was selected from Action drop down. An Output File name was chosen and import was complete. Import wizard was closed. Now, user reopens Import Table Data again and runs another import. In the last screen, the "Save SQL statements to file" option is preselected, however, the Output File field is disabled and populated with the file name of the previous import.
Change Action type and reselect "Save SQL statements to file" option to enable Output File field.
Waiting for fix to be released in a future version of Toad for Oracle.