When i was executing my script i often found NL-runtime-01 error on specific type of file extension like (.woff) or .css.
This error is generic. You should check the NeoLoad log files accessible through the menu "Help-->Open logs folder..." to get any more details.
Does it only happen when you run a test or also when running a check virtual user?
You can also check the LG log files that are displayed in your test result under the logs tab.