In:

  ~/.emacs.d/init.common.el

which is attached, there's a (debug) call around line 150.
init.common.el is called by ~/.emacs, which is also attached.
After this line is executed, the *Backtrace* buffer is as
shown in the next attachment.  After 2 d's in the *Backtrace*
buffer, it shows as in the next attachment.

At this point, I've not a precise location of where the
debugger is in the emacs code.  There are no "source code"
windows showing this.  How can I see where the debugger
is now located in the source code?

After the next d, the top of the *Backtrace* shows:

> Debugger entered--beginning evaluation of function call form:
> * (quote c-insert-my-tab)
> * (define-key c++-mode-map (quote tab) (quote c-insert-my-tab))
>   c++-mode-my-hook()
>   run-hooks(c-mode-common-hook c++-mode-hook)

So, I guess the debugger will soon be in c-insert-my-tab (defined
in the 1st attachment).  So, I hit d again and get the following:

> Debugger entered--returning value: c-insert-my-tab
>   (quote c-insert-my-tab)
> * (define-key c++-mode-map (quote tab) (quote c-insert-my-tab))
>   c++-mode-my-hook()
>   run-hooks(c-mode-common-hook c++-mode-hook)

Which is not much help; so, I hit d again and get:

> Debugger entered--beginning evaluation of function call form:
> * (byte-code "ÁÂÃ!\"‡" [err message "File mode specification error: %s" prin1-to-string] 4)
>   normal-mode(t)
>   after-find-file(nil t)

Which tells me nothing about what code is being executed.
Hitting d again gives:

> Debugger entered--entering a function:
> * prin1-to-string((wrong-type-argument arrayp tab))
> * byte-code("ÁÂÃ!\"‡" [err message "File mode specification error: %s" prin1-to-string] 4)
>   normal-mode(t)
>   after-find-file(nil t)

which doesn't help much.

Finally, I hit c, resulting in the top *Backtrace* containing:

> Debugger entered--returning value: "(wrong-type-argument arrayp tab)"
>   prin1-to-string((wrong-type-argument arrayp tab))
> * byte-code("ÁÂÃ!\"‡" [err message "File mode specification error: %s" prin1-to-string] 4)


Please, how can I find out what's causing this error message:

  "(wrong-type-argument arrayp tab)"

TIA.

-Larry