I can't properly compile this tutorial level. When I do, I receive the following message:

"This map requires one or more textures that can't be found. Replace with default textures?"

If I select "Yes", my sky is filled with stone tiles.
When I attempt to make the sky brighter or darker by pressing 1 or 2 the following error message pops up:

Malfunction W1501
Empty pointer in bright_lights: sky_cube_level.blue+=10

There seems to be something missing in this workshop level.
could somebody please help me?

Here's the example code for the workshop 13 level
////////////////////////////////////////////////////////////////////

var video_mode = 7; // 800x600 pixels

////////////////////////////////////////////////////////////////////

function bright_lights()
{
sky_cube_level.blue += 10;
sky_cube_level.green += 10;
sky_cube_level.red += 10;
}

function dim_lights()
{
sky_cube_level.blue -= 10;
sky_cube_level.green -= 10;
sky_cube_level.red -= 10;
}

function main()
{
on_1 = bright_lights;
on_2 = dim_lights;

level_load ("work13.wmb");
while (1)
{
if (key_w == ON)
{
camera.tilt += 1;
}
if (key_s == ON)
{
camera.tilt -= 1;
}
if (key_a == ON)
{
camera.pan += 1;
}
if (key_d == ON)
{
camera.pan -= 1;
}
if (key_lastpressed == 19) // if [R] is pressed
{
camera.pan = 0;
camera.tilt = 0;
sky_cube_level.blue = 128; // medium brightness
sky_cube_level.green = 128;
sky_cube_level.red = 128;
}
wait (1);
}
}

This tutorial requires version 6.40 or above.

What is the size and date of your standard.wad file? It could be from an old version and does not contain the required sky_gorge texture.

Same here, even update to A6.50.2, some textures are
missed in the standard.wad. In my case, workshop19,
the "floor001" texture is missed.

My standard.wad size = 9,734KB, date = 29/04/2004.

There seems to be a big urge to post "me too" posts no matter the topic. But don't worry, in your case the standard.wad size and date are absolutely fine. There is no "floor001" texture in the standard WAD. You can just compile Workshop 19 with replacing the missing texture by the default texture. But you're right, we'll add an existing texture.

I'm using version 6.50.2.
The script should work for let's say the texture "skywhite" too, shouldn't it? I just have to texture the sky cube with it and set the "sky" flag and compile the level.

No. "Skywhite" is not a sky cube. You need to use the very texture mentioned in the tutorial, and not something else.

Well, the texture mentioned in the tutorial is not supplied with the tutorial.

Well, read my first response.

Sorry. My standard.wad file is 9734kb in size and dates from 29.04.2004 11:31.

Yes, that's the right one, so you have that sky texture.

Check that this file is available to your Workshop 13 project - "Standard.wad" must be visible on a bar in the WED texture view, and must contain the sky_gorge texture. You can activate displaying the texture names by right clicking into the folder window. If it's not there, you've probably accidentally removed it from the project, or have copied an older standard.wad file into your workshop location, or are using another, older Gamestudio version somewhere on your PC.