As much as it seems natural to me, I'm abandoning the "Quote/Response" method. Things are getting a bit too strung out and probably hard to follow, so I'll first summarize, just to weed out the extraneous stuff that's gone before:
So far, the following tests were requested and yielded the following results:(Note that xxxxxxxx is substituted for the actual user name in all shell snippets.)
1.) Attempt to launch PCManFM from a regular user's shell prompt:[xxxxxxxx@localhost ~]$ pcmanfm %U
[xxxxxxxx@localhost ~]$ This resulted in no feedback in the shell, and only a dialog box which stated, "Error - No such file or directory."
2.) Check of permissions for /home/xxxxxxxx using ls -ld /home/xxxxxxxx:[xxxxxxxx@localhost ~]$ ls -ld /home/xxxxxxxx
drwx------ 116 xxxxxxxx xxxxxxxx 4096 Sep 10 17:23 /home/xxxxxxxx/
This resulted in the directory listing given in the second line of the shell snippet above, showing the permission on this user's account.
3.) Neal provided the permissions for a user account on his machine for comparison:drwxr-xr-x 69 me me 4096 Sep 11 04:33 /home/me/ We should note the differences in permissions here. It looks as though my user's ~/ folder lacks some permissions in comparison to the one Neal provided. This may be the crux of the matter - missing permissions on my user's home folder? (Thanks for that data, Neal.)
Neal was good enough to give a brief explanation of %U and why we use it.%U = user
In other words, "pcmanfm %U" will open PCManFM as the user logged in to the terminal. When you launch an app that opens in your home, you need it to be told to open in your home and not the home of some other system user.
{and, further on in the discussion}
Menu entries are provided through the use of .desktop files. Each .desktop file has an Exec= line in which the launch command for that app is provided. ...
On a single user system, an app like PCManFM can be launched without the %U. Still we use it. Why? Because it tells the app to open at /home/user.
This brings us to the present.
Neal has requested a further test, namely the following ran from a normal (non-root) user's shell:pcmanfm /home/xxxxxxxx This resulted in PCManFM starting very quickly with no attending error. (Basically, this was the "work-around" I mentioned earlier.)
At this point, I'm going to go out on that limb again, and modify the permissions of my ~/ directory to match those of Neal's, just to see what happens:
[xxxxxxxx@localhost ~]$ chmod go+rx /home/xxxxxxxx
[xxxxxxxx@localhost ~]$ ls -ld /home/xxxxxxxx
drwxr-xr-x 116 xxxxxxxx xxxxxxxx 4096 Sep 10 17:23 /home/xxxxxxxx/
(I included another check afterward with ls -ld to "prove" the new permissions.)
Trying to launch pcmanfm %U from a non-root shell after this still results in no feedback on the terminal and the dialog with "Error - No such file or directory".
Question: is it possible
I'm actually missing a file or directory somewhere? (I smell another, "Well, Duh!" moment coming.

)
Another possibility: Might I have needed to do something like...
chmod go_rx -R /home/xxxxxxxx to recursively extend these permissions to all subfolders of /home/xxxxxxxx? (NO... I haven't tried that yet. Not at all sure that would be right.)
Oh, and as to the suggestion advanced by Ferdes Fides? I'm not sure it is applicable in my case. The duplicated wallpaper entries he mentioned do not appear in any of my pcman.conf files (I have two, one in ~/.config/pcmanfm/default, and the other in ~/.config/pcmanfm/LXDE). I have entries for "wallpaper0" but none for just "wallpaper"
(Uh... I remember he deleted "wallpaper0" entries. Hmm. Maybe I'll edit my "wallpaper0" entries....)
Since I need to log out and log back in to test this last S.W.A.G., I'll stop here for now, and updated in a P.S. Until then...
Later On,
D
P.S.: No joy. pcmanfm %U still refuses to launch and still throws the "No such file or directory" error.
Neal - let me know if I need to undo the last two things I tried, please. Thanks again for helping sort this out. - D
It just occurs to me I have left out a symptom? Nope, looking back I mentioned it in the original post, but it bears repeating:
On log-in, the "desktop" displayed does not show any shortcuts or my selected wallpaper, just a brushed grey metallic background similar to that used for the default login screen.