The boards apparently consider thread titles ending with the word 'print' to be printer-friendly view. This also means you can't reply to them, edit them, etc.
Hm. Last time, editing the thread's title fixed the problem. However, under the current forum software, that doesn't seem to help (for some reason, it doesn't change the URL, which probably is what's needed to fix it). As such, I'd recommend creating the thread again - just make sure 'print' isn't the last word in the title.