This error is typically related to the Easy Anti Cheat software. Please try and install or repair the EasyAntiCheat software. 

You can do this by going to C:\Program Files (x86)\iRacing\EasyAntiCheat (or C:\Program Files (x86)\Steam\steamapps\common\iracing if you purchased and installed through Steam) and run the set up file from there by right-clicking and selecting Run As Administrator. 

If after that you are still having this issue, please look in your Documents/iRacing folder and see if you have a file in there called sim_launch.txt. If you do, please email this to support@iracing.com. 

Also, look in your Documents/iRacing/logs folder and send us any log files that are in there. 

Also, can you provide the loader.log from the following location after one of the failures? 

C:\Users\YOURNAMEHERE\AppData\Roaming\EasyAntiCheat\36 

If you cannot see that folder, you can paste the following text into the explorer bar and it will navigate you there. 

%AppData%\EasyAntiCheat\36