To the best of my knowledge, that is the last build of TRS 2006. It isn't a service pack. It was included here in the states with Trainz Railwayz. Not much different that can be seen but that the Rail Exchange link was removed from the start up menu. It had not worked for some time. I'm sure there might have been some bug fixes but no new features that I have seen.
TRS2006 had only SP1.
TRS2004 had SP1, SP2, SP3 and SP4.
TS2009 has had SP1 so far.
Before anyone asks, I don't know of a way to update TRS2006 SP1 to this build number other than buying it and replacing your current version. Not worth the effort in my opinion.
William
W