Well, one of two things comes to mind:
1) There was a mistake/omission in the export
2) The RV8 just doesn't accept skins.
You've got a layered RGB file. Flatten the layers, change it to indexed 256 color (aka 8-bit) and save it as a bitmap.
or
Take the bmp you already exported for the RV8 and put it onto a p51 or something. It'll look like garbled crap, but if it shows up as garbled crap you know the bitmap *itself* is fine. If it crashes then you know it's the bitmap. If not then you know it's the RV8.