Added debugging info to mifconv.exe 'Bug 1414 - mifconv system() call to svgtbinencode seems to have a timing issue with Raptor 2.9.2+', which seems to alleviate the symptoms...
<?xml version="1.0" encoding="UTF-8"?>
<SystemDefinition schema="3.0.0">
<package id="platformtools" name="Platform Tools">
<collection id="gfxconversion" name="Graphics Conversion">
<component id="bmconv_s60" filter="s60" name="S60 Bitmap Converter">
<!-- component need to be moved to appropriate location -->
<unit bldFile="/tools/platformtools/gfxconversion/bmconv_s60/group"/>
</component>
<component id="mifconv" filter="s60" name="Multi Icon File Converter">
<!-- component need to be moved to appropriate location -->
<unit bldFile="/tools/platformtools/gfxconversion/mifconv/group"/>
</component>
</collection>
</package>
</SystemDefinition>