In Quark 6.6 beta 7, after one or some mouse clicks, you may get this error.
The player skin was showing in the game, but the error in Quark editor was shown. Doesen't matter that the file roarke.pcx was not here in this game folder, by default, temporary or not.
Put it here from pak0.pak from your roarke mod folder. You must rename it to skin.pcx after you close your Quark editor.
Renaming roarke.pcx to skin.pcx after you close your Quark editor
The skies will be made for windows to look trough and for parts of the ceilings.
The textures are .png or .wal, 256X256 resolution and the images are tiled.
.png if not animated and .wal file type if they are animated.