Ok, I looked into your shader code and probably found the bug. Its unrelated to 6.4 and also unrelated to the bitmap size.

function eff_initWater()
{
//enable: Use mipmap stages
//help: This enables mipmapping on pixelshaded water surfaces.
//help: Note: Mipmaps may slow down the rendering process on
//help: older graphics cards.
define mips;

bmap_to_cubemap(mtl.skin1);
ifdef mips;
bmap_to_mipmap(mtl.Skin1);
endif;
.....

Replace this by:

function eff_initWater()
{
bmap_to_cubemap(bmap_to_mipmap(mtl.Skin1));
.....


You have to create mipmaps _before_ converting your texture. A converted texture has a different format. Mipmap creation just overwrites it and renders it unuseable.

Most 3D cards just ignore the mipmap instruction here, but your GeForce card obviously attempts to create mipmaps and thus destroys the environment effect.

The same, of course, applies to normal, bump, tangent, or other special bitmaps.