Arsalan and Michael, I am very grateful for your support. I have now got it running as I want!

Hello Peter, I am sorry for what you going through in your relationship. Life is hard and its like that don't worry and I hope things will be sorted for you.

If you still struck after trying Michael suggestion below, what we can do is to help you and setup it for you. You can send us details in email or a contact form.

Okay, now that there's obviously nothing worth to backup anyway I'd suggest to
1. remove any files from the 4 directories you mentioned
2. in order to verify your domain mapping is working correctly at all
a) create an index.html file inside of httpdocs
containing a single line like 'this is my production site'
b) create an index.html file inside of dev.localapp.live
containing a single line like 'this is my development site'
3. Access localapp.live and dev.localapp.live from your browser and asure the output appears as expected

I am afraid I have got confused and screwed up my system completely by moving backup files around and overwriting stuff. I tried starting from scratch and get to the error "ossn:exception:title"

I think I am distracted by my partner being discharged from a local mental ward and she is rejecting me after a 5 year relationship during the latter part I had been caring for her...

That's brilliant and clear to me. Thank you.

Why you copying when you setting up development copy? just re-install a fresh on development copy?
Since you are now moving please follow https://www.opensource-socialnetwork.org/wiki/view/999/how-to-move-ossn-installation-to-another-server-and-domain

I have copied the premium files from my pc to the new sub domain and have created an empty new database. There is now a new ossndata directory called ossdev_data. However, when I try to navigate to the new sub domain, the system picks up the existing system. Is the system sensitive to directory structure on the server?

The present files structure is:
localapp.live
....httpdocs (containing the current software system)
....ossndata
....dev.localapp.live (containing the copy software system)
....devossn_data (empty)

I could move the dev.localapp.live directory to its parent directory to be on the same level as localapp,live.

Having installed the software in the root of the domain, I find I cannot recreate it in the sub domain. Is it possible to set things up now just using the sub domains?

Why you can not able to re-create it? is it something restricted by your provider? You can also do

1. ProDomain.com
2. dev.prodomain.com
3. devdoamin.com
4. prodoamin.com

Many possibilities

Having installed the software in the root of the domain, I find I cannot recreate it in the sub domain. Is it possible to set things up now just using the sub domains?

I'll see if we need both instances to be on sub domains, or whether one can be the main domain.