I see your post has no response for a while. You stated you are new here, so I don't want you to feel like you are being ignored; although I'm sorry to say that I do not have a direct answer to your question.
I checked the Allaboard website, but saw no reference to "AO Sub", nor can I think of any actual subdivisions abbreviated with "AO". Also, I don't recall any reference to the "AO Sub" with the original RWA Lakeside route, so I'm thinking that the extended version's requirement for the "AO Sub" would be insignificant at best.
My advice would be to install the route, disregarding the "AO Sub" requirement, and see if any "milk bottles" are visible. If you are not familiar with the term "milk bottles"; these are the little icons, shaped like an old fashioned milk bottle, that indicate the location of a missing object. As long as it is not something critical to the route's operation, trackage for example, then (if I recall correctly) you could always go into the route editor and replace the milk bottle with an object that is in your inventory. Then again, any milk bottles you find, might be so far away that they are unnoticeable. You could also run the route's file through "Trainsim Tools" to identify any missing objects.
Let us know how it goes; especially if you are still having problems. Perhaps someone else can provide a better answer. Good luck and welcome to RWA
