Cubemaps and skybox resolution

[Trude]

The last post on this was old enough to warrant a new topic.
When building cube maps, the console returns the standard error:

Skybox vtf files for <name> weren't compiled with the same size texture and/or same flags!
Can't load skybox file <name> to build the default cubemap!

Various sources say this is often caused by a bug and suggest various workarounds. These did ultimately work, but I'm still curious as to what triggers the error in the first place.
When texturing a world brush with a 2D skybox, it displays a size of 128x128 near the texture select toolbar. Does this mean that the skybox defined in the map properties needs to be 128x128 as well?

[Zeq]

I am not 100% sure of this but I believe it is something like this:

Skybox vtf files for <name> weren't compiled with the same size texture and/or same flags!
Usually when making skybox textures you want all 6 sides to be sqaure and of the same size. In the case of many valve skyboxes though, some sides are often rectangular and of different sizes. For these skyboxes valve has included the vmt command "$basetexturetransform" which will basically offset this, but it will still produce an error when building cubemaps.

Can't load skybox file <name> to build the default cubemap!
Some games have a default cubemap stored in the game files, but TF2 doesn't. So it produces this error when trying to build it.

Both of these errors are common and harmless as far as I know.

Check out this tutorial to make sure you are building your cubemaps correctly:
http://forums.tf2maps.net/showthread.php?t=16452

[Trude]

Both of these errors are common and harmless as far as I know.
http://forums.tf2maps.net/showthread.php?t=16452

I read this is a common bug and it ultimately does not effect building cubemaps when using a workaround. I'd just like to eliminate the error for completion's sake.