Well we know the file directory is correct.
Please confirm the BMP name in that directory.
Then see what happens when you load the skin viewer, choose spit9, then choose the spit9_1 drop box under the plane selection. Does it show?
EDIT: Also check the SIZE of the file. A 1024x1024 bitmap will always be the same filesize at 8-bit, regardless of what pixels you put in there.
Mine say: 1.00 MB (1,049,654 bytes)
If it's significantly LARGER then the file is surely RGB or millions of colors and that explains it. Perhaps a google tutorial search for GIMP about exporting or saving files. The above screenshots are all I know, and those seem to work for my version.
