[texworks] can't find file

[L.A.D. de Boer]

Dear members,
I'm new to this list. I searched the archive for "can't find file" but 
did not find my problem.

I just transferred my LaTeX files from my Win-pc with Texworks to my 
Ubuntu-pc with Texworks.
My main file is /home/lou/TexDocs/Fundamentals/main.tex
Its first line reads   \input{../hdrBook.tex}
Compiling stops immediately, error: can't find file. (On the Win-pc 
compiling went fine)
It concerns the header file /home/lou/TexDocs/hdrBook.tex .
I also copied the header file to the directory Fundamentals and tried
   \input{hdrBook.tex}and
   \input{hdrBook}and even
   \input{/home/lou/TexDocs/Fundamentals/hdrBook.tex}
But alwasy the same error: can't find file.
Desperately I also added a path /home/lou/TexDocs to edit>preferences> 
typesetting>paths .
What should I do?

Thanks, Lou