I installed it as in the readme.txt file. I added the scenery in add-on and I added the area in the scene library. The scenery is for FSX. And not only for the scenery that I posted link but also the came screen occured in Poland scenery and in the others. I searched a lot but I didnt find any solution.

(
http://www.sanalpilot.com/downloads/marmara.zip I downloaded from this link).
As you asked for help on this forum I naturally assumed you downloaded the scenery from Simviation. I downloaded the file from your link to check it out. The instructions are not in English but from what I can make out this scenery appears to be for FS2004. That might be the cause of your problem.
marmara scenery
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Aciklama ve kurulum
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marmara.zip icinde cografya folderi, istanbul folderi ve rakamli 4 bgl dosyaysi vardir (HL955170.bgl, HP955170.bgl, RD955170.bgl, ST955170.bgl).
1. cografya folderi icinde marmaranin cofrafya datasi vardir. Bu folderin altinda sadece scenery folderi vardir. Cografya folderini Program Files\Microsoft Games\Flight Simulator 9\Addon Scenery klasorune yerlestirin
2. istanbul folderi icinde uc boyutlu modeller vardir. Bu folderin altinda scenery ve texture folderlari vardir. istanbul folderini Program Files\Microsoft Games\Flight Simulator 9\Addon Scenery klasorune yerlestirin
FS2004 ana menusunde settings/scenery library/add area fonksiyonu ile bu iki folderi FS2004e tanitin daha sonra fs2004 u tekrar calistirinca sceneryler aktif olacaktir.
3. HL955170.bgl, HP955170.bgl, RD955170.bgl ve ST955170.bgl default FS2004 temel cografya datasini degistirmektedir. Bu uc dosyayi :\Program Files\Microsoft Games\Flight Simulator 9\Scenery\asia\scenery yerlestirin. Mevcut dosyalari overwrite etmek (uzerine kopyalamak) gerekecektir. Bu nedenle bu islemi yapmadan once FS2004 un orijinal (Default) HL955170.bgl, HP955170.bgl, RD955170.bgl ve ST955170.bgl dosyalarini Flight Simulator 9 klasoru disinda bir klasorde backup olarak muhafaza etmeniz tavsiye olunur
PS. Note that it also involves overwriting default files which are probably different in FSX.