Change texture

I'm having problems changing the loaded textures dynamically.

My project is based on image targets. 

I need different textures loaded based on marker. I cannot load all textures, that will use alot of memory.

If I load the textures on start they show ok:

for (int i = 0; i < nTextures; ++i)

            [textureList addObject: [NSString stringWithUTF8String:textureFilenames[i]]];

If I detect another marker I want to change textures (simplified code, just changing one texture but same problem)

Texture *tex = [[[Texture alloc] init] autorelease];

NSString *file = @"newtextureimage.png";

[tex loadImage:file];

[textures replaceObjectAtIndex:0 withObject:tex];

Object3D *obj3D = [[Object3D alloc] init];

obj3D.numVertices = NUM_PLANE_VERTEX;

obj3D.vertices = planeVertices;

obj3D.normals = planeNormals;

obj3D.texCoords = planeTexCoords;

obj3D.numIndices = NUM_PLANE_INDEX;

obj3D.indices = planeIndices;

obj3D.texture = [textures ObjectAtIndex:0];

[objects3D replaceObjectAtIndex:0 withObject:obj3D];

[obj3D release];

After texture is changed the object is all black.

The texture is known good. If I try to change in reverse order the texture is ok and after change black.

Any suggestions?