ntdll.dll error?

What is ntdll.dll? Every now and then I get an error when editing a route and this ntdll.dll error message comes up?
https://railworksamerica.com/forum/
https://railworksamerica.com/forum/viewtopic.php?f=29&t=18519
AmericanSteam wrote:Did you recently a NVIDIA driver update just before this started?