[NTG-context] Adobe ArnoPro in mkiv

Hi all, I'm trying to use the Adobe ArnoPro font (just testing if it will work with ConTeXt). The font does work with ConTeXt/XeTeX, but not in mkiv. When I try to compile my test file with mkiv, I get this error message (which isn't very helpful to me): (/home/tas/texmf/tex/context/type-arnopro.tex (/home/tas/texmf/tex/ context/type-arnopro.mkiv)))) MtxRun | return code: ? ...live/texmf-local/scripts/context/lua/mtx-context.lua:572: attempt to compare number with nil I'm using the latest beta and luatex 0.28.0 Can anybody explain what's going wrong here? Thanks Thomas