You may find the answer to this issue in this forum thread:

Please try and uncheck in compatibility "admin mod when executing" "iracingsim64dx11.exe"


If you still have this issue, please try and uninstall and then reinstall the iRacing software. The best way to reinstall iRacing is to first remove it from your Control Panel...Add/Remove Programs. 
Then delete the C:\Program Files (x86)\iRacing folder.
Empty your Recycle Bin.
Then reboot your computer. After that, log back into iRacing and follow the download/install/update instructions. Although your setups and replays should not be affected in this process, if you feel more comfortable, you can first back up your My Documents/iRacing/Setups and Replay folders first.
To save time (and bandwidth), you can back up your C:\Program Files\iRacing\Cars and Tracks folders to another location. Then after deleting and reinstalling the iRacing program, before doing the download/updates - replace the new Cars and Tracks folders with the original ones. Then go back to the iRacing Members site and click Refresh. You may still need to do a small update but it will be much quicker. You can also find this information in our FAQ: CLICK HERE
You may also find this forum thread helpful:
Are you an admin on the PC? If not this can also cause this error.
The last thing to try is turning off UAC. It’s in your control panel under user accounts.
If you are still having this issue after that, you can try is create a new Windows User (as admin) and then install iRacing as this new user and see if that helps. If not, you may consider reformatting your OS.