yeah... just that.
I don't know why you still get crashes - I just installed the heg beta, then download the "RS2_Environment_for_Hegemonia City States.rar", unzipped it into my bi/hcs/data folder MINUS the "world" folder, chose to overwrite, deleted my map.rwm (in bi/hcs/data.../base), fired up the heg beta and went straight for a custom battle in potidaia - no crash
did I do something wrong (or right)???
EDIT: GOT IT!!!
I played the first battle with a settlement - and all was well, since the settlement provided a land square for the armies to fight on
I tried it without a settlement - and my men appeared in the middle of the ocean! They drowned and "game over"
Since I hadnt played potidaia in "vanilla" heg beta, I can't be 100% sure, but as I didn't change my base map folder, I'm half certain that it's just a matter of potidaia having been matched to wrong map coordinates in the custom_locations.txt file (the coordinates correspond to a sea square)
If I'm right, there's nothing wrong with the RS2 environment addon!

It's just a "vanilla" glitch!
EDIT2: I just posted on the bugs thread about this...
DON'T delete your map.rwm - not unless you make a backup of it.
You will probably have problems starting a new campaign - the re-generated map.rwm presents some "misalignment" with the campaign's definition and I get kicked out to main menu...
EDIT3:
And one last edit - install heg beta, install RS2 environment addon MINUS the world folder; DON'T delete the map.rwm. If you want to play "potidaia" edit the entry in the custom_locations.txt file (in the data folder) so that the coordinates are (259 124) instead of (257 124). Everything else plays fine!
Kudos to toon for the conversion (and RS2 for the art) - excellent job!

Lovely environments for our heg hoplite battles!