How can I make the Island of Lesbos settlement-compatable???

[Makanyane]

Re -show_err, right click on your desktop shortcut you use to launch game, select properties, in 'Target' line type
space minus show underscore err
after end " finished result should look like:
"X:\xxxx\xxxx\Rome - Total War\RomeTW-BI.exe" -show_err

(you got this far without that one!)

As you're going back to menu you should get show err message now when you quit - how helpful it will be is another matter - you're quite likely just to get a couldn't create settlement message which can have variety of causes!

Re: your island, check on corrected_regions.tga (in .exe level folder) that the city pixel is actually appearing on land mass, if not you might need to make island bigger in map_heights.tga - to get that used you need to delete map_heights.hgt from campaign folder (if there) and base (assuming you're on 1.5 / 1.6)

You only need to delete the map.rwm in folder that contains your map .tgas (thats where new one will be generated) but you may as well delete / rename the one in base anyway. Also if you launch and get kick back to menu you will probably have generated a new map.rwm you need to keep deleting that each time you make change.

Could be that, that island has invalid ground type for settlement - basically you can't put city on anything troops can't walk on - impassable forest or mountains - and you're meant to have some fertile ground type for every region.
I can't visualise where you mean at the moment if its still not working can you screenie the map_regions and point it out?