I’ve just sent a minor update of the release version of
siunitx to CTAN. There was a clash with the
fourier package, to do with maths fonts. This is all due to the lack of an upright μ in Computers Modern: a continued pain. For the moment, all is sorted again! One note: I’ve done the release here using TeX Live 2009, rather than my more usual MiKTeX 2.7. Everything seems to have worked, but any feedback is of course welcome!