This isn't a technical answer at all, but what I did was:
1. clicked on the link you provided
2. when the webpage opened, I looked at the web address in my URL bar
3. replaced "grail-trail" with "threads" in the URL bar and reloaded the page
I figured this out by manually finding the thread you inquired about and copying that current URL and then comparing to the URL you posted and finding the difference.
We lost a lot of threads like this when the website was upgraded last time due to a change in the forum software. Nothing that could be avoided unfortunately. Not sure if it is a fix or not, but if it one, Don can get it straight.