What does this cubemap error mean for TF2?

Garry's Mod mapping
#1

I got this when trying to build cubemaps for a night version of pl_badwater. All of the reflections are purple and black checkers.

*** Error: Skybox vtf files for sky_night_01 weren’t compiled with the same size texture and/or same flags!
How would I fix this?

#2

Means that the skybox textures weren’t made the same.

#3

How would one solve this problem?

#4

I presume they are custom, so just remake them with vtfedit and make sure that they all have the same settings.