[GNC] "No suitable backend" error for database backed gnucash file

[coolnodje]

Using Gnucash on MacOS, I got this error trying to open a recently
created file which I think I based on a database back-end instead of the
standard.

I have upgraded to 3.0 in the meantime and thought it was the problem.

But I realized when I finally was able to start a v2.6.20 on an older
MacOS10.12 virtual machine that I still had the problem.
Which means that this is all unrelated to the 3.0 upgrade.

I've tried to revert the file to an older version (prior to the last
modification, so prior to the last successful opening) but got the same
error.
This really confuses me:

- the file as it was the last time it was successfully modified cannot
be opened (which should exclude file corruption problem)

- the latest version on latest MacOS can't open it because "No suitable
backend", but 2.6.20 on MacOS10.12 also can't open it because "No
suitable backend".

So if the file itself is not the problem, and if version that used to be
able to open it can't anymore, where could the problem come from?

Only I wasn't able to reproduce the error with the exact same setup I
had when last successfully modified: trying to reinstall 2.6.20 on
MacOS10.13 I realized it can't be started anymore (Gnucash can't be
opened because of a problem - DYLD, [0x4] Symbol missing)

Is there anything I can do to try to save the file in question?

- nodje