Normally, nXtRender registers its commands with AutoCAD during installation. On occasion, this mechanism may fail. In this case you will need to manually load nXt the first time you run it in a particular version of AutoCAD.
Use the following procedure:
Type _appload at the command line.
Navigate to the folder where nXt was installed. This is normally C:\Program Files\AccuRender nXt
Select one of the following files depending on your platform:
For example, you should be able to load the one named AccuRender nXt_22_64.arx for AutoCAD 2018 or AutoCAD Architecture 2018, on a 64 bit computer.
Check the AutoCAD command line to verify that the application loaded without error. At this point you should be able to type nxt or ar5 to launch the application. You should not have to repeat this procedure again for this version of AutoCAD. Simply typing nxt or ar5 at the command prompt should cause nxt to load. You may need to repeat this procedure if you install another version of AutoCAD.