Interesting, I just looked at the BMP. Since there are almost no large areas of the same color, it looks like the graphics will not be compressed too well. That could cause the size of the resulting vgaspec to be too large (unfortunately, I haven't figured out yet what the size limit would be) and consequently lead to problems in CustLemm.
Can you tell me how large the resulting vgaspec file is?
I'll probably have to take some time to fix the compression in myvgaspec so that it compresses better. In the meanwhile, talk with Mindless. He has a program that can recompress DAT files, and generally results in smaller sizes than even the compression used by Psynosis. That might allow your vgaspec to work.
That being said, I don't think that particular graphics of yours will work too well as an actual level anyway, even if there are no issues.