Earlier today the forums were down for a while due to a disk space issue. In the process of investigating it, we discovered that our forum software is no longer open source. This means that upgrading the software is not possible.
In order to provide a way forward with the forums, we are going to have to migrate to another application. We'll be working on migrating all the data and users over this week, and next weekend (Friday 20 October) we will be switching over to the new forums.
Sorry for the inconvenience, and thanks for your patience!