I need to know exactly what distribution you're using on your Raspberry Pi, including distro name and release.  Simply Fortran for Raspbian was last build with Raspbian 8 (Jessie) for maximum compatibility.   There's a good chance that dependencies have broken in more modern versions with Simply Fortran 2.41.  We don't test on anything but Raspbian, though, on the Raspberry Pi.

If you send the a problematic project file, I can take a look at why it's crashing.

I have managed to compile, link and load one project, by using a text editor to edit the .prj file.
I wasn't able to open my other .prj file, however, because trying topen a .prj file from inside SF causes it to crash.

I have therefore opened the other ,prj file in SF by double-clicking its name from outside SF, which loads SF and then opens the project.  From within this second .project, in which I have NOT yet been tinkering with the .prj file, I tried to add a source file.  Immediate crash.  This seems to show that the fault not connected to anything I have done in the .prj file.

As all the .prj files in my RPi are in projects I am porting from Windows, I am wondering whether this shows that the problem is unconnected with the .prj file, but I can't think where else to look.

This has been a sudden change in SF's behaviour, so it must be the result of something I’ve done, but I don’t know what, I haven’t been able to fix it, and if you are able to recognise the cause, maybe you could put in an extra error trap in future updates.  Details below.

I can't be sure of exactly how and when it started so please don't attach too much to the following but I have been trying to port a Windows project into Linux and I think it /**/might/**/ have started whilst I was (1) looking at the .prj files and the makefile, to try to see where the .prj file was pointing to things in my Windows file structure that are in a different place in my Linux file structure, (2) searching for case sensitivity problems with INCLUDE files, (3) trying to correct the Options>Project>FIleLocations>SearchDirs entries and (4) that kind of thing.

I have done all the usual things to try to cure the problem, like
- checking file ownership and permissions,
- closing all, shutting down rebooting,
- manually deleting all .o  and .mod files, and the makefile.
- selecting 'Always generate Makefile',
. uninstalling SF completely, and re-installing it.

The symptoms

THESE ACTIONS DON'T CRASH SF
Opening an extg project by clicking its name on SF's opening screen.
Opening an extg project in SF by double-clicking its name from outside SF.
Project>Save Project.
Files pane>right-click>Disable/enable file.
Project>Add folder.

THESE ACTIONS DO CRASH SF, EVERY TIME
Project>Open project [ie I can't open a project by this method)
Opening screen>Recent projects>Import
Options>Project>FileLocns>SearchDirs>ADD
Files pane>right-click>Add new file
Project>Add new file
Project>Add file(s)

THESE ACTIONS DON'T CRASH SF BUT THEY DON'T WORK
Options>Project>FileLocns>SearchDirs>[select an entry]REMOVE
(this doesn't remove the unwanted entry; Project>save doesn't help )

I seem to have broken SF2.41, and I can's seem to mend it, not even by un/re-installing.  The problems are not trivial.  They are making SF unusable.  I suspect that there is a simple solution, like deleting something somewhere, and I'm  still searching for it, but if you could help me Jeff (or ANYone!),, I'd be grateful. 
---
John