make installworld problem

[OxY]

hi!

i just wanted to upgrade one of my servers to 6.1-release, used cvsup to
fetch 6.1-rel, then 
make buildworld
make buildkernel
reboot
mergemaster -p
make installworld

but when i start make installworld i got error...
i tried to delete the whole /usr/obj and did a make buildworld again, didn't helped..
dunno what's the matter, on other machines this problem doesn't appear..

here's the error log:

seismic-10 root# make installworld
mkdir -p /tmp/install.MXqa872H
for prog in [ awk cap_mkdb cat chflags chmod chown  date echo egrep find grep install-info  ln lockf make mkdir mtree mv pwd_mkdb rm sed sh sysctl  test true uname wc zic; do  cp `which $prog` /tmp/install.MXqa872H;  done
cd /usr/src; MAKEOBJDIRPREFIX=/usr/obj  MACHINE_ARCH=i386  MACHINE=i386  CPUTYPE=  GROFF_BIN_PATH=/usr/obj/usr/src/tmp/legacy/usr/bin  GROFF_FONT_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/groff_font  GROFF_TMAC_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/tmac  PATH=/usr/obj/usr/src/tmp/legacy/usr/sbin:/usr/obj/usr/src/tmp/legacy/usr/bin:/usr/obj/usr/src/tmp/legacy/usr/games:/usr/obj/usr/src/tmp/usr/sbin:/usr/obj/usr/src/tmp/usr/bin:/usr/obj/usr/src/tmp/usr/games:/tmp/install.MXqa872H make -f Makefile.inc1 reinstall
make: Permission denied
*** Error code 126

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.