Never had this problem. Can`t help you there, sorry.
Try a virus scan first, I`d say.
Did you google it? Lots of infos about what it is and where it belongs to.
I find the dll in a folder of a benchmark for example or in the 3DSMax folder.
It belongs to the Embree Ray Traycing Kernels.
On Github you find the Embree Example Renderer for all OSes.
You might want to download the *.zip archive for your OS and install it, perhaps?
Maybe that fixes the problem.
Or: do a search in the registry and find out where it is/was registered.
Could give you some hints too.
Other then that Terragen staff should be able to tell you if it really is needed for the software.
Good luck.
cheers, Klaus
