When I try and configure .config with xconfig it breaks (see below) for source from 2.6.15-rc6-git3 . Make menuconfig works.
[root@localhost linux]# make xconfig HOSTCXX scripts/kconfig/qconf.o scripts/kconfig/qconf.h:25: error: extra qualification ConfigSettings:: on member readSizes scripts/kconfig/qconf.h:26: error: extra qualification ConfigSettings:: on member writeSizes scripts/kconfig/qconf.h:127: error: extra qualification ConfigList:: on member updateMenuList make[1]: *** [scripts/kconfig/qconf.o] Error 1 make: *** [xconfig] Error 2