But why a new thread? Are we still discussing the same grinding issue?
When you say "first time", are you new to 4wd in general, or just new to the 4wd system in the Pathfinder? I applaud wanting to learn in either case.
Keeping in mind what I mentioned on the other thread, there should be little or no grinding unless there's a legitimate problem with gear meshing. Assuming that's not the problem, are you sure you understand the shifting process?
Does the truck have manual front hubs? If so, and these are not engaged, you will have difficulty engaging and disengaging.
If you don't have a copy of your Owner's Manual, here you go:
http://justgivemethedamnmanual.com/down ... finder.pdf
From it:
(You do have an AT, right?)
There's more information in the manual beyond this. It behooves you to read it.
If this still doesn't work, then there may be a real issue.