SOLUTION FOUND:

Just though I'd update this thread - The answer is obvious now I've seen it. The error log shows
".../var/www/ossndatadiruser/1/profile..."

should be:
".../var/www/ossndatadir/user/1/profile..."

Updated in ossn.config.site.php and wham! sorted

Thanks!

Good, that's already one hint, that the image is not in place - but gives no idea why.

As I posted already recently: Teaching how to setup up a Linux box as a "hosting provider instance" is beyond the capabilities of this forum. You're on your own or you have to consult the Ubuntu community.

But since you're working with a virtual instance anyway, I'd suggest trying something like the Turnkey Lamp Stack instead ( https://www.turnkeylinux.org/lampstack )

It still needs some twisting here and there, but a lot is already working out of the box and you got at least a nice administration panel.

Thanks for that - I am with the machine now. Error Log says:

[02-Mar-2017 13:43:28 UTC] PHP WARNING: 2017-03-02 13:43:28 (UTC): "filegetcontents(/var/www/ossndatadiruser/1/profile/cover/f907a34b9768b446bcea3f328ce904ec.jpg): failed to open stream: No such file or directory" in file /var/www/html/ossn/components/OssnPhotos/ossn_com.php (line 374)

Thanks!

Either your data directory is not writable or your images are too large.
Enable error reporting and install the System Info compoment to retrieve more details.