[OS X TeX] figures in ConTeXt

[Dalyoung]

Hi all,

I hope that it is not OT in this list to ask about ConTeXt.
I am testing ConTeXt in XeTeX.
I tried to put two figures side by side following the manual. But the 
error message appeared.
Here are  the code and the error message.

\placefigure
  [here]
[fig:pentano]
  { Pentagon }
\startcombination[2*1]
	{\externalfigure[pent1]}{}
  	{\externalfigure[pent2]}{}
\stopcombination

! Missing { inserted.
<to be read again>
                    \let
\noshowargumenterror ->\let
                             \expectedarguments \noexpectedarguments
\dodoubleempty #1->\noshowargumenterror
                                         \doifnextcharelse 
[{\dodoubletestemp...
l.46 \startcombination
                       [2*1]
? x
No pages of output.

After I commented out \startcombination[2*1], I got the output. But two 
figures appeared vertically. I copied code from the 
manual(mp-cb-en.pdf, p25).
What is wrong with this code?
Thank you for reading.

Regards,

Dalyoung

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