Unicode works in mkii but not in mkiv

I have been using texexec which, as I understand it, is mkii. I have several documents that have unicode in them and typeset perfectly using texexec. However, texexec seems to have trouble with metapost and I would like to use mkiv. However, when I use context only a handful of the unicode characters actually typeset, namely the capital greek characters.

Any ideas why? How can I fix this?

Example In the following, the alpha typesets using texexec but not context.

\starttext
α
\stoptext
-
A minimal example is needed. In general, ConTeXt MkIV handles unicode much better than MkII –  Aditya Sep 18 '11 at 1:15
@aditya I added an example. –  Doug Moore Sep 18 '11 at 1:22