These are the steps you can take:

• Slow down to below 100kph till the error disappears
• Ensure that the car has enough transmission fluid 
• If you haven't serviced the gearbox for the last 50,000km or more, do so by changing the gearbox oil with original recommended oil for the gearbox.
• If the problem persists, change both the gearbox oil and sieve. You can also consider adding an extra radiator / cooler specifically for the gearbox. This is usually way smaller than the usual car radiator.