[NTG-context] Blackboard bold \Bbb and MKIV

Hi all, In my first steps in experimenting MKIV, I typeset the following minimal example \starttext Let ${\bf c} \in {\Bbb R}$. \stoptext with luatex, but the Blackboard Bold {\Bbb R} doesn't appear. The same file is fine with MKII. LuaTeX gives hundreds of warnings such as: luaTeX warning (file /usr/local/gwTeX/texmf.local/fonts/map/dvipdfm/ context/original-ams-base.map): invalid entry for `msbm10': both ps_name and font file missing (for various fonts), but I don't know what are exactly the differences between the ways of handling fonts in MKII and MKIV. For your information the above are obtained under: ConTeXt ver: 2008.02.11 10:35 MKIV fmt: 2008.2.12 int: english/ english Thanks for your attention: OK