Some time ago i needed a forum software and took a look at the open-source-community. There were a lot of forums out there the most used is phpBB. The installation worked fine and everything was fine. The only thing was that there was no file upload/download function within the forum.
But after googeling around for a while i found a common mod for implementing this functionality. The installation of the mod was a damned hard thing, i had to edit about 20 files. Alternatively you could install already patched files, but the problem was that my forum was already installed and configrured, and so i would have to reconfigure it.... But after that it worked.
Some weeks after launching the forum a new version was released. Nothing big, so i followed the installations-instructions and they said that i had to reinstall all mods.... damn... the other possibility was to patch the files automatically. It took me a long time to install this patch. After some more weeks another patch was sent, and i realized that the mainenance of this forum costs a lot of time.
The next problem that occured was when my provider called me, some script tried to cheat around in my account. The vulnerability was.... phpBB... so i shut down the forum. But there were a lot of people that wanted to have access to the old messages, so i began to look to an alternative forum, and came across the Simple Machines Forum (SMF). I know this forum because Joomla, my favourite CMS is using it.
So i gave it a try, and installed it, it looked fine, easy to install easy to maintain, with the possibility to install and unistall mods automatically, very fast and very good looking :-)
And by accident i came across an migration-script from phpBB to SMF, and also gave it a try.... and could not believe it, the users, rights, threads, forums, attachments!!! were migrated and still working! My forum is up again and enhanced with several mods like a chat-mod and other nice features.
I can just recommend this software.