"Master file already set" instead of compilation

[Janusz S. Bień]

Hi!

I'm confused and annoyed by the following problem.

I have two documents with the identical structure: a short master file
inputs the actual text. The local variable blocks are analogical.

In one document C-c C-c in the included file works as intended. In the
second one it gives the message "Master file already set".

I will appreciate your suggestions how to diagnose the problem.

Best regards

Janusz

Emacs  : GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-09-23, modified by Debian
Package: 11.91

current state:
==============
(setq
 AUCTeX-date "2017-07-24"
 window-system 'x
 LaTeX-version "2e"
 TeX-style-path '("/var/lib/auctex/emacs/" 
"/usr/share/emacs/site-lisp/auctex/style" "/home/jsbien/.emacs.d/auctex/auto"
                  "/home/jsbien/.emacs.d/auctex/style" "auto" "style")
 TeX-auto-save t
 TeX-parse-self t
 TeX-master nil
 TeX-command-list '(("TeX" "%(PDF)%(tex) %(file-line-error) %(extraopts) 
%`%S%(PDFout)%(mode)%' %t" TeX-run-TeX nil
                     (plain-tex-mode ams-tex-mode texinfo-mode) :help "Run 
plain TeX")
                    ("LaTeX" "%`%l%(mode)%' %t" TeX-run-TeX nil (latex-mode 
doctex-mode) :help "Run LaTeX")
                    ("Makeinfo" "makeinfo %(extraopts) %t" TeX-run-compile nil 
(texinfo-mode) :help "Run Makeinfo with Info output")
                    ("Makeinfo HTML" "makeinfo %(extraopts) --html %t" 
TeX-run-compile nil (texinfo-mode) :help
                     "Run Makeinfo with HTML output")
                    ("AmSTeX" "amstex %(PDFout) %(extraopts) %`%S%(mode)%' %t" 
TeX-run-TeX nil (ams-tex-mode) :help "Run AMSTeX")
                    ("ConTeXt" "%(cntxcom) --once --texutil %(extraopts) 
%(execopts)%t" TeX-run-TeX nil (context-mode) :help
                     "Run ConTeXt once")
                    ("ConTeXt Full" "%(cntxcom) %(extraopts) %(execopts)%t" 
TeX-run-TeX nil (context-mode) :help
                     "Run ConTeXt until completion")
                    ("BibTeX" "bibtex %s" TeX-run-BibTeX nil t :help "Run 
BibTeX")
                    ("Biber" "biber %s" TeX-run-Biber nil t :help "Run Biber")
                    ("View" "%V" TeX-run-discard-or-function t t :help "Run 
Viewer")
                    ("Print" "%p" TeX-run-command t t :help "Print the file")
                    ("Queue" "%q" TeX-run-background nil t :help "View the 
printer queue" :visible TeX-queue-command)
                    ("File" "%(o?)dvips %d -o %f " TeX-run-dvips t t :help 
"Generate PostScript file")
                    ("Dvips" "%(o?)dvips %d -o %f " TeX-run-dvips nil t :help 
"Convert DVI file to PostScript")
                    ("Dvipdfmx" "dvipdfmx %d" TeX-run-dvipdfmx nil t :help 
"Convert DVI file to PDF with dvipdfmx")
                    ("Ps2pdf" "ps2pdf %f" TeX-run-ps2pdf nil t :help "Convert 
PostScript file to PDF")
                    ("Glossaries" "makeglossaries %s" TeX-run-command nil t 
:help "Run makeglossaries to create glossary file")
                    ("Index" "makeindex %s" TeX-run-index nil t :help "Run 
makeindex to create index file")
                    ("upMendex" "upmendex %s" TeX-run-index t t :help "Run 
upmendex to create index file")
                    ("Xindy" "texindy %s" TeX-run-command nil t :help "Run 
xindy to create index file")
                    ("Check" "lacheck %s" TeX-run-compile nil (latex-mode) 
:help "Check LaTeX file for correctness")
                    ("ChkTeX" "chktex -v6 %s" TeX-run-compile nil (latex-mode) 
:help "Check LaTeX file for common mistakes")
                    ("Spell" "(TeX-ispell-document \"\")" TeX-run-function nil 
t :help "Spell-check the document")
                    ("Clean" "TeX-clean" TeX-run-function nil t :help "Delete 
generated intermediate files")
                    ("Clean All" "(TeX-clean t)" TeX-run-function nil t :help 
"Delete generated intermediate and output files")
                    ("Other" "" TeX-run-command t t :help "Run an arbitrary 
command"))

-- 
             ,   
Janusz S. Bien
emeryt (emeritus)
https://sites.google.com/view/jsbien