3826462 - Error: "The following message from the reservation system may help them in assisting you: ND TL/TKTG"

I selected the flights by schedule and priced the flights. Once I click on reserve and continue page,  we get the following error message "We were unable to save your changes to this itinerary. If you continue to have problems, please contact your travel administrator or your travel agency. The following message from the reservation system may help them in assisting you: ND TL/TKTG"

When booking Air, some times we get the following message from the reservation system "ND TL/TKTG" , KBA , CON-CA-ADM , Administration , CON-CA , Cross Applications , Problem