Found out why. I think a thread of yours had been moved that's all. So when you click the link to it, you get redirected to the Aussie forum where it has been moved to.
Edit: No I think you are just logged out on the device you're getting the message on.
So when you're logged out, and come from Aus, or USA, or Canada; you get a notice at the top of the forum (mainly there for Search Engine Optimisation reasons but it's also helpful) saying that we have a forum specifically for you.
We were on a .co.uk domain name for 12 years. So whilst we had some traffic from overseas, it wasn't much. We switched to a global domain (.net in this case) and I stuck a notice on the forum so that no matter what page you're on, we link you to the forum setup for you.
So A) that means you are logged out on that device - it only shows to logged out people, and
B) your username is taken, by you.
So you just need to login on that device.
This is the login page:
Log in - https://www.electriciansforums.net/login/
Click login at the top of the forum (not register) if you can't get to this thread etc. If you want I can email you a link to the login page. Then you can click that and login on the other device. Then check the box to stay logged in (if it shows) and you're sorted.
You can post in any forum you want though. Usernames and Avatars on the forums all have flags next to them so UK guys know when they're in a AU thread.