Hi,

For this example with simsun.ttc (it can be download from
http://www.slax.org/modules.php?action=detail&id=2630):

\definefont[song][name:nsimsun]
\starttext
\song 测试
\stoptext

ConTeXt MkIV said:

fonts           > fallback modern rm 12pt is loaded
system          > begin file b at line 3
fonts           > otf loading > loading:
selfautoparent:texmf-local/fonts/truetype/winfonts/simsun.ttc (hash:
simsun-nsimsun)
fonts           > otf loading > font loaded okay
fonts           > otf loading > loading failed (file read error)
fonts           > defining > forced type ttc of simsun not found

I have tested the uming.ttc (AR PL UMing, it can be download from
http://www.freedesktop.org/wiki/Software/CJKUnifonts/Download) and got
the same error.

--
Best regards,

Li Yanrui