A fresh install was the easiest way to go for now. I installed 2.6.3 LTS for a change to see what differences there may be between this and old faithful 2.9.
The Startup Disk Creator took just 6 minutes to flash the ISO to USB stick then approximately 15 minutes to install the system and another 15 minutes (coz I like playing with how things look) to get my system looking the same as my other laptop.
Updates carried out, AWN panel initiated, Firefox prettied up the way I like it.
All OK.
So what's next... well tomorrow I'll have to try the VirtualBox VMs to see if simply copying them back will work. This 2.6.3 system is only 32 bit and the last system was 64 bit. Fingers crossed but, I have a sneaky suspicion I may either have to reinstall with the 64 bit version of 2.6.3 (it does come in 64 bit doesn't it?) or reinstall VirtualBox and set-up the virtual machines again.
Fun or what...
At least the problem with the 'Authentication Failure' MessageBox has gone.