This is a common problem with routes sold by RSC and almost all "3rd party" routes as well that include moderate to large yards: the entire yard is a single signal block. The only route I know of that is an exception to this sad state of affairs is the VNHRR, which has numerous hidden signals throughout the large yard at Springfield. That said, the warning that two or more trains share the same signal block does not necessarily mean that those trains will not run successfully: sufficient patience with scenario editing will allow more than one train to occupy a block successfully -- until they don't. What I mean is that in an yard without signal blocks, our friend the mythical dispatcher seems to throw the dice every time a scenario runs: some AI trains run as planned, others not.
I speak with authority on this subject because I've spent many hours of this past week trying to bring one of the scenarios I wrote for the Altoona Yard on the Horseshoe Curve route up to 2014 standards -- assuming that there are any. One problem is that the HC doesn't seem to have been updated. Another is that only three signal posts exist within this large yard and they seem to hinder more than they help.
My advice is to keep plugging away, be prepared for lots of arbitrary disappointments, and once your scenario runs successfully twice in a row publish it quickly.
