Right then, the log in trouble has been resovled, by undoing the upgrade of the software.

Having done some more research into the matter I've discovered that there is an unfixable break with the software that allows logging in to the main site and the forum at the same time. You can read on to find out more of the gory details if you like. For now though, it's looking like we'll have to not upgrade the website software, which isn't great as it leaves it open to attack.    

The front end of the website (the homepage with the news and the showcase areas) and the forum area are two different pieces of software. The frontend is called Joomla (www.joomla.org ) and the forum system is called SimpleMachines Forum (www.simplemachines.org ). What I did to join these together is use a thing called a 'bridge' which allows one bit of software to interact with the other, and use the same database of user data, so you can log in to both with one username and password.

Both pieces of software are OpenSource software, meaning they are free to use. However Joomla have recently decided to change the terms of their license under which the software is distributed and how it interacts with other software. So from the latest release (1.0.13) of Joomla onwards, there will no longer be any support for simplemachines, which operates under a different license. 

In layman's terms, this represents a big fat smelly pooh!

One choice we have is to leave Joomla sat at 1.0.12 version. In terms of functionality this isn't really an issue as it does everything we need. The issue comes with security concerns. The longer we leave the website on an old version the more likely it is some 14 year oik will choose to exploit one of the known vulnerabilities witin the software and hack our site. 

The other options we have is either to move away from SMF forum system to something compatible with Joomla, or to move away from integrated frontend and forum log in systems.

I'd welcome your thoughts if you have any on this slightly arcane area of web lore. If you have any thoughts, please do share them in the forum. 

Ta,

Evan