Comment 3 for bug 501154

@Alvin - do you know if Inkscape 0.47 now includes UniConvertor 1.1.4 or still 1.1.3? AFAIK PLT support was only added in version 1.1.4 which would explain the failure.
I cannot reproduce it with a similar file (containing a simple path and a linked bitmap (raster) image): the image is silently dropped and the vector object correctly exported (besides the known scaling issue) with UniConvertor 1.1.5 prerelease. Same when exporting to *.hpgl: the bitmap image is ignored and all vector information is correctly exported.

@Robert - your file doesn't contain any vector information - I doubt that a plotter could handle raster images that haven't been vectorized (http://en.wikipedia.org/wiki/HPGL). So even if UniConvertor supported PLT on win32 the file 'wk.plt' would be empty.

    <image
       y="353.36218"
       x="238.85715"
       id="image2826"
       height="358"
       width="368"
       xlink:href="file:///C:/Bert/wk.bmp" />

If the same error happens when exporting to *.wmf of *.sk1 - please attach the bitmap file as well so we can test it on other platforms (Inkscape 0.47 uses UniConvertor as helper application to export to *.plt, *.wmf, *.sk1). It could possibly be related to
Bug #487410 “export to EMF or WMF omits images from graphic”
Bug #492904 “Won't save as .wmf file with .jpg inserted in drawing”