The cab editor is for editing the position of controls, not changing the cabview or editing the textures. To edit the textures use TGAtool2 from the file library at train-sim.com to convert the .ace files in the Cabview folder to .tga, then open in Photoshop, PSP, Paint, or someother photo editing program. Then backup the old .ace files and save the files you repainted back as .ace files. You also have to use or make an alpha channel if you want to see out the windows, ask here if you need more help with that.
To fix the problem with it not loading the textures, go back to the Cabview folder and change the files you changed to .cvf, back to .ace again and it will load.
EDIT: I know this is a old post, but it was never answered.