source-registry configuration

[Greg Bennett]

Running under Linux Mint 18.1 64 bit, and either ccl or sbcl

Apologies, I'm afraid I have made a mess of configuring the path to some 
.asd files.

I believe that items 3,4,6,7,8 of Section 8.1 Configurations do not exist.

I believe I have used item 5 as in Section 4.1 Configuring ASDF to find 
your systems.

In ./config/common-lisp/source-registry.conf.d I once created the file 
gb-lisp.conf
containing the single line
(:tree "/home/gwbennett/asdf-tests")  <- no trailing /
instead of (:tree "/home/gwbennett/asdf-tests/")    <- trailing /

I have since replaced that file with source.conf holding just the line
(:tree "/home/gwbennett/asdf-tests/")

In the asdf-tests directory there is a file gb-a.asd and associated lisp 
files

When I try
(asdf:load-system "gb-a")
I get (under ccl64 Version 1.11-r16812M)
 > Error: Is a directory : #P"/home/gwbennett/asdf-tests"
 > While executing: CCL::MAKE-FILE-STREAM, in process listener(1).

Under sbcl 1.3.18 I get an analogous message, always pointing to the 
same pathname.

If I remove the .conf file completely, restart either lisp, retry the 
load-system, the error persists.

Some how I seem to have managed to get the incorrect specification 
squirreled away in asdf's memory
in a way which survives not just restarting either lisp, but restarting 
linux too.

What in the world have I managed to do ? More usefully, how do I undo it ?

Thanks for advice and assistance.

Cheers  Greg Bennett