I couldn't find on this forum anywhere that Mike had followed up on this thread with the research we did later.
(I'll post it here since I'm not allowed to post at UKTS anymore.

)
After removing the unnecessary Provider/Product (P/P) entries (which is now built in to RW_Tools) we found that we could not get into the scenario editor for some scenarios on some routes. We tracked this down to the total amount of P/P content that is "called" for a particular Route/Scenario combination. The biggest problem was caused by the Kuju\RailSimulator\Railvehicles and/or Kuju\RailsimulatorUS\Railvehicles folders because they tend to be quite large.
I started with a Kuju\RailSimulator\Railvehicles folder of 9.93 Gb and a Kuju\RailSimulatorUS\Railvehicles folder of 1.91 Gb. The first one was so large because I had downloaded and installed a lot of reskins that I'd never used.
What I did was to move each of these folders aside and use RW_Tools to identify which folders were necessary for the scenarios that I had installed. (Mike added a new button that lists all stock used in all scenarios and can be used to identify the missing ones.) (After I have moved the necessary folder back into the Kuju folders, I ran the "Check selected stock for missing files" RW_Tools routine to identify other items of stock that were needed to satisfy some dependencies.)
When I finally got all of the "missing" stock back in the Kuju folders, I had a Kuju\RailSimulator\Railvehicles folder of 4.36 Gb and a Kuju\RailSimulatorUS\Railvehicles folder of 0.9 Gb. I haven't had an SBHH since, running the game, the route editor or the scenario editor.
Our conclusion was that TS2013 will produce an SBHH if the total size of the P/Ps called by a route/scenario combination includes too much "stuff". (I called it "stuff" because we're not quite sure what TS2013 loads from the P/Ps that are called. We haven't figured out how much is too much either.)
Bob Latimer.