Eclipse might need to be launched with Administrator privileges (right-click on eclipse.exe and run as Administrator).
To install the Custom action in NeoLoad, you need to copy your Custom Action:
lib/extlibdirectory of the NeoLoad project if the project is collaborative or will be exported to NeoSense
extlibdirectory of your
<install-dir>folder if the Custom action will be used in several projects
extlibdirectory of the
<install-dir>folder, right-click on your Java project and select Run As > Maven install.