Do you have ‘Write’ permissions for the File/Folder/Dir you’re saving to?
of course I have. Most of the times KiCad disappears, but sometimes not.
Salvatore
Are the drive you’re saving to local ? There has been issues reported when network drives are used.
… intended for debugging, not for fixing…
• Look at the folder contents of a Successfully opened/saved and Quit project.
What files are in the project after quitting?
Compare to a Failed project…
EDIT - Adding clarifying info:
• Open Kicad, Create a new project
• Run PCBnew from main panel
• Add a Footrpint (Just go through the motions of it but, don’t actually place it on the board or, if placing it, delete it, cancel adding it. File>Save_As_Copy (don’t rename it)
• Do same for Eeschema
Quit Kicad and look at folder contents - what are the files added?
no, it is a Synology NAS but, as already wrtten, sometimes it happens, sometimes not. The path is in UNC format.
Salvatore
ahh… there’s a reason I asked about permissions but didn’t go further.
An old post of mine talked about filenames and the Encoding and Kicad NOT liking any other than UTF-8. I kept having access problems… Until I fixed that (and, Don’t use graphic text characters! like bullets… etc. Keep the name unified (no spaces)
project name: Prova. The files in the folder are the usual ones:
Prova.pro
Prova.sch (no components added)
Prova.sch-bak
Prova.kicad_pcb (no footprints added)
Prova-cache.lib
fp-info-cache
Strangely, making a “Save as” without renaming in PCB triggered the overwrite confirmation request, but didn’t produce a .bak copy, that instead happened with Eeschema. A bug?
Salvatore
KiCad has some NAS related trouble:
Windows Specific Issues
Network Shares
Editing projects located on Windows networks shares provided by samba servers (non-Windows Server, i.e. Synology, FreeNAS) may result in crashes due to samba generating bad file change events and our cross-platform toolkit asserting the invalid event rather than ignoring it. Windows Server hosted shares should not encounter this issue.
You will have to work on a local drive if you encounter crashes working from a network drive for now. More details can be found in GitLab Bug #5740.
Probably not a Bug, just the way coder did it.
EDIT - Notice the Bak file is sch-bak… The hint is sch=eeschema and fp=footprint.
Footprints are used in PCB…
So, you discovered the files and they’re now in the folder. You should now be able to use without problems. Does it work?
If you use a Template, observe the files and ensure the two Cache files are present…
I have read the post, but it doesn’t concern to my case. I only use characters [a…z, A…Z, _, -] and maybe some other allowed non alpha characters for project names (Windows 10 environment). The particular project of which I’m talking about in this post is named CPU001, so no spaces either, but the “full path” contains spaces:
\FILE_SERVER\cartelle_comuni\Documenti personali\Elettronica\Progetti\ANNIBALE\Schemi\CPU001\KiCad
Now I cannot rename the “Documenti personali” folder otherwise I should change a myriad of projects and library paths. But could it be “that one and only space in the path” the cause of the problem?
Salvatore
get rid of the Spaces in the Path!!! (I see only one but, it takes only one Terrorist to ruin your day
oh, I see. But it happens that when I add or modify libraries and footprints that are located in the same base folder, but some subfolders behind:
\FILE_SERVER\cartelle_comuni\Documenti personali\Elettronica\KiCad\sb\library
KiCad never closes itself. It happens only with projects. Very strange indeed, isn’t it?
Salvatore
aaaaaaaargh, I have to change the whole world! 
I haven’t only KiCad under “Documenti personali”… I’m not in a hurry, so it would be preferable to wait a fix for this. Is it possible?
Salvatore
So, you discovered the files and they’re now in the folder. You
should now be able to use without problems. Does it work?
it works, also the other real project works, but as soon as I try to save: BANG! But not always, as already written.
Salvatore
I’m only a dumb user - the real supporters can talk to the underlying problem.
That said, after discovering the problem, I had to rename everything as all of my Directories did not use UTF-8 fonts and some had spaces…
I was easy to Bulk change them, though. Example: Select All of your Folders, select the name (or fragment of the name) and “Use Selection for find” then, “Replace All” with corrected text…
Me thinks the problem lies in the File/folder name. AND, when I started to fix my system, it ALWAYS had some files that Crashed! I needed to completely redo the Folders… That fixed it
I had to rename everything
it is not a matter of a simple “rename”, I have the “whole world” under “Documenti personali”… 
, that means other 48 folders and subfolders, not only “Elettronica”…
Salvatore
Well, lessons learned - I’m old-school and often get bit when violating the “Eight” character filenaming requirement from 40 yrs ago… Sure, new technology has improved, but, as seen here, not always… Something to do during Covid shutdown…
Check https://gitlab.com/groups/kicad/code/-/epics/33 for several network drives related bug reports as well
mmmh, I also started in 1979 with my first home made Z80 computer running CP/M 
As you can see in my second message in this post, I catched an entry in the Windows registry with this error:
Codice eccezione: 0xc0000005 <— should be an access violation
Offset errore 0x0000000000154e23
ID processo che ha generato l’errore: 0x2134
Ora di avvio dell’applicazione che ha generato l’errore: 0x01d6c335addb0e03
Percorso dell’applicazione che ha generato l’errore: C:\Program Files\KiCad\bin\kicad.exe
Percorso del modulo che ha generato l’errore: C:\Program Files\KiCad\bin\wxbase30u_gcc_custom.dll
What is wxbase30u_gcc_custom.dll?
Salvatore
I see. Is this problem expected to be fixed in incoming v6?
Salvatore