cvsup to 6.0 stable from 5.5 release

[Rick Knospler]

I keep getting this error when I try to make build world on version 6.0..
--------------------------------------------------------------
 >>> stage 1.1: legacy release compatibility shims
--------------------------------------------------------------
cd /usr/src; MAKEOBJDIRPREFIX=/usr/obj/usr/src/tmp  INSTALL="sh 
/usr/src/tools/install.sh" 
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:/sbin:/bin:/usr/sbin:/usr/bin 
WORLDTMP=/usr/obj/usr/src/tmp  MAKEFLAGS="-m 
/usr/src/tools/build/mk  -m /usr/src/share/mk" 
/usr/obj/usr/src/make.i386/make -f 
Makefile.inc1  DESTDIR=  BOOTSTRAPPING=502010  -DNO_HTML -DNO_INFO 
-DNO_LINT -DNO_MAN -DNO_NLS -DNO_PIC  -DNO_PROFILE -DNO_SHARED 
-DNO_CPU_CFLAGS -DNO_WARNS legacy
ERROR: Source upgrades from versions prior to 5.3 not supported.
*** Error code 1

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

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

Stop in /usr/src.

I am running version 5.5...

(12:20:10 <rick at star:/usr/src>) # uname -a
FreeBSD star.skylands.net 5.5-PRERELEASE FreeBSD 5.5-PRERELEASE #0: 
Thu Mar  2 21:54:14 EST 
2006     rick at star.skylands.net:/usr/obj/usr/src/sys/GENERIC  i386

How can I get past this error and upgrade to 6.0 stable..?

Thanks