Many forum posts contain URL references to other forum posts. For an example, see http://www.trains.com/trccs/forums/834613/ShowPost.aspx which refers folks to another post. Often, these links point to helpful information previously posted. However, all of these embeded, member-posted forum links are now broken because Trains.com has changed how each of these topics are referenced in the upgraded version of the forums.
I work in IT and understand that sometimes such references need to be changed. However, what needs to be built and run by Trains.com on a one-time basis is a conversion program that will swamp out all of the broken URL forum references with correct URL forum references. Yes, this will take some programming work, but without it, the knowledge base that has been assembled in the forums has lost a significant amount of value and utility. I am surprised that Trains.com's IT staff or consultants did not anticipate this and plan accordingly. Hopefully, it will be corrected.