I do exactly what you told me (For sure). However, the game dont even work. Here's the DataBase error window pops up

buildingbuildtxt 639. Expected string ID
buildingbuildtxt 639. warning:require field Product Cost missing
buildingbuildtxt 639. warning:require field Upkeep Cost missing
Unable init the Data bases

1) building.txt

############################################################

IMPROVE_SEWER_SYSTEM {
DefaultIcon ICON_IMPROVE_SEWER_SYSTEM
Description DESCRIPTION_IMPROVE_SEWER_SYSTEM
EnableAdvance ADVANCE_INDUSTRIAL_REVOLUTION

PrerequisiteBuilding IMPROVE_IMPROVE_AQUEDUCT

ProductionCost 900
Upkeep 4
ProductionPollutionPercent -0.15
PopulationPollutionPercent -0.15
}

############################################################

2)Unit.con

ICON_IMPROVE_SEWER_SYSTEM { FirstFrame "UPIP048L.TGA" Movie "NULL" Gameplay "IMPROVE_SEWER_SYSTEM_GAMEPLAY" Historical "IMPROVE_SEWER_SYSTEM_HISTORICAL" Prereq "IMPROVE_SEWER_SYSTEM_PREREQ" Vari "IMPROVE_SEWER_SYSTEM_STATISTICS" Icon "UPIP048L.TGA" LargeIcon "NULL" SmallIcon "NULL" StatText "IMPROVE_SEWER_SYSTEM_STATISTICS" }

Note:
-since there is no UPIP047L.TGA so i use it to replace the secity monitor
-I have sewer sys icon in CTP2/gamedata/grafic/picture

3)BuildingBuildingList

BUILDING_BUILD_LIST_HAPPINESS {
Building IMPROVE_SHRINE
Building IMPROVE_THEATER
Building IMPROVE_ARENA
Building IMPROVE_BASCILICA
Building IMPROVE_MOVIE_PALACE
Building IMPROVE_SEWER_SYSTEM
Building IMPROVE_RECYCLING_PLANT
Building IMPROVE_PUBLIC_TRANSPORTATION
Building IMPROVE_TELEVISION
Building IMPROVE_ECO_TRANSIT
Building IMPROVE_MATTER_DECOMPILER
Building IMPROVE_VR_AMUSEMENT_PARK
Building IMPROVE_BODY_EXCHANGE
}

4) gl_str.txt

IMPROVE_SEWER_SYSTEM "Sewer System"

5) Great library.txt

[IMPROVE_SEWER_SYSTEM_PREREQ]
Requires:
ATABASE_ADVANCES,ADVANCE_INDUSTRIAL_REVOLUTION>Industrial Revolution

Cost: {BuildingDB(Building[0]).ProductionCost} ATABASE_CONCEPTS,CONCEPT_PRODUCTION>Production
Upkeep: {BuildingDB(Building[0]).Upkeep} ATABASE_CONCEPTS,CONCEPT_GOLD>Gold
[END]

[IMPROVE_SEWER_SYSTEM_STATISTICS]
Gives:
{BuildingDB(Building[0]).ProductionPollutionPercent}% ATABASE_CONCEPTS,CONCEPT_POLLUTION>Pollution (from Production){BuildingDB(Building[0]).HappyInc} ATABASE_CONCEPTS,CONCEPT_HAPPINESS>Happiness
{BuildingDB(Building[0]).PopulationPollutionPercent}% ATABASE_CONCEPTS,CONCEPT_POLLUTION>Pollution (from Population)
[END]

[IMPROVE_SEWER_SYSTEM_GAMEPLAY]
The First improvement to fight pollution
[END]

[IMPROVE_SEWER_SYSTEM_HISTORICAL]
Data Not available
[END]

IMPORTANT NOTE;
You need to leave the line of text
Description DESCRIPTION_IMPROVE_
to something that is already in the game. I believe it is a holdover from CTP1, but if you change that line to your new addition, it will not work. At least I haven't been able to get it to work. It does not affect gameplay though.

Change your entry
Description DESCRIPTION_IMPROVE_SEWER_SYSTEM

to
Description DESCRIPTION_IMPROVE_MOVIE_PALACE

Movie Palace is part of the default setup.

I had made the same mistake when first attempting to add buildings/governments/units. The instructions that were given to me did not include that bit of info. I almost gave up at that point. As it appears, your problems are the same. Make the change and the game should launch. The files for units/wonders/governments also have the same type of line of text.

Immortal Wombat also has a possible workaround to this problem, which he had posted in the thread where my instructions are, though I haven't tried it yet.

Martin
The DATABASE error was due to a mistake on my part, but this forum did not recognize the particular sequence of text on that line. You will see the same error on your post. The word DATABASE is showing up as ATABASE. I had attemped to edit my earlier post to bypass that discrepency, but I must of missed that additional character.

After looking at your reply and the works on your modification, I fixed my mistakes. As for the game, it works perfectly . As for Martin Gühmann sugestion, It helps to fix problems on the Great Liberly text.

I think Wes has something tied into Wonders with units, so you could drop him an email asking about it.