Please check that the correct date, time, and time zone is set correctly.
Please do the following:
1. Open Windows Control Panel (small icons view), and click on the Date and Time option.
2. Click on the Internet tab from the top.
3. Click on the Change settings button.
4. Click Yes if prompted by UAC.
5. Check the box next to Synchronize with an Internet time server.
6. Select the server from the drop-down list and click the Update now button.
7. Click Ok to finish.
Then log out and back into iRacing.
You may be seeing this error also if you are trying to launch a TT or a session in a series that we do not offer during Week 13 (the week in-between seasons). 2021 Season 4 will begin the night of March 14th.
Another reason is most of the Dirt series we do not offer TTs for so if you are trying to access a TT for a Dirt series, you may see this error as well.