This error occurs when duplicate cases have been manually entered into the eFileTexas system.
However, the clerk allows only one case to be valid and considers any additional cases to be null. Selecting only of these "null" cases results in the "Unknown filing codes" error.
If you search for the case number again for which you received this error, you will see more than one case display. Select one that you did not choose with the previous submission attempt and start a submission based on it. You should not experience the error this time.