[OS X TeX] Error when trying to use the beamer style

[John Maindonald]

I've just started trying to use the beamer package again, after a lapse
of several months.  Whatever I try, even the simple beamerexample1,
I am getting the message

(/usr/local/teTeX/share/texmf.gwtex/tex/generic/pgf/basiclayer/ 
pgfbaseimage.cod
e.tex)) (/usr/local/teTeX/share/texmf.gwtex/tex/latex/pgf/utilities/ 
xxcolor.sty
! Undefined control sequence.
<argument> \XC at mcolor

I have updated my latex installation, using i-installer, but to no  
effect.
I am using the 2005 installation, but that has not changed since I
started using beamer.

Any clues?   Other things work fine.
John Maindonald

John Maindonald             email: john.maindonald at anu.edu.au
phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
Mathematical Sciences Institute, Room 1194,
John Dedman Mathematical Sciences Building (Building 27)
Australian National University, Canberra ACT 0200.

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