If all you have is one folder, you have to cut and paste the contents of that folder. This should include the .biq folder (which will show up as the scenario), a folder of the same name and a readme file.
Looks like you are missing a file, so it is still using one of your old set. I have used Snoopy's since it came out and no problems.
Or could be a landmark terrain tile is still the old set.
Advanced Tactics is not in the basic game, you must be playing a scenario.
That could be a land mark terrain tile, looks like the lxpgc.pcx file.
Make a copy of your xpgc.pcx file and rename it Lxpgc.pcx, then replace your current lxpgc.pcx file with the newly named file.
You may have to do this for all the terrain files that begin with L, I seem to remember having this probel with LM terrain when I first used Snoopy's terrain.
Edit: I just downloaded and opened Snoopy's terrain and there are no LM terrain files.
To make them yourself, just copy all of Snoopy's x*** files and rename them lx*** and put them in the conquests/terrain folder.
And because the art assets for Conquests is split between the art directory in vanilla Civ and Conquests, do I need to replace the art directories in both places?
But remember that those versions of Sn00py's terrain don't have Volcanoes or Marshes!