i think if there getting textures from battle arena that is a custom thing somone has done?
Loading textures from another map is a native function/feature of realspace 2 (aka gunz), maiet did it where applicable.
To load textures from another map add "../" infront of the map and texture name in the diffuse map.
For example;
"../garden/gzd_map_Garden_mask.tga" as diffuse map will make the game load the texture "gzd_map_Garden_mask.tga" from garden.
../ = go up once in the current folder hierachy, mrs files are treated as folders essentially so ../ will make the game leave your maps folder into the clients maps folder where it then looks for garden and within for gzd_map_Garden_mask.tga to load it.
Since quest maps arent in the maps folder but their own maps folder (by default/originally anyways, some servers changed that while organizing files differently), they have multiple ../ to escape/change the current location.
Example;
../../../maps/dungeon/gzd_map_DG_wreckage01.bmp would make the game follow this route
Gunz/Quest/Maps/Dungeon_passage1.mrs ../ -> Gunz/Quest/Maps/ ../ -> Gunz/Quest/ ../ -> Gunz/ -> Gunz/Maps/ -> Gunz/Maps/dungeon/gzd_map_DG_wreckage01.bmp
Some mrs packers can corrupt textures and other files occasionally which can cause your issue.