After adding cygwin ports mirror (kernel.org) to setup.exe and running it several times to install various packages (for example sox), I frequently see this error at the end:

Package: Unknown package
glib2.0.sh exit code 1

The relevant lines from the install log appear to be

2011/02/22 10:47:01 running: C:\cygwin\bin\bash.exe --norc --noprofile /etc/postinstall/glib2.0.sh
Error opening directory '/usr/share/glib-2.0/schemas': No such file or directory