make release cross-platform: Malformed conditional (${MK_SENDMAIL} != "no")

I'm trying to build a -CURRENT install cdrom, using the following command:

make release CHROOTDIR=/usr/current \
        EXTPORTSDIR=/usr/ports \
        CVSROOT="/home/ncvs" NO_FLOPPIES=YES \
        NODOC=YES NOPORTS=YES MAKE_ISOS=YES \
        KERNELS_BASE=GENERIC TARGET_ARCH=amd64 \
        BUILDNAME=7.0-20060909-SNAP


from a XEON server running 6.1-STABLE FreeBSD Thu Sep  7 13:42:16 CEST 2006

First question (reality check): is it possible to build 7-CURRENT(amd64) 
on 6-STABLE(i386)?

If yes, do you know what may be the cause of the error I get after the 
'build world' phase? (please see attachment for make output)

   cd /usr/src/release/../etc && make distrib-dirs 
DESTDIR=/R/stage/trees/base
   "Makefile", line 6: Malformed conditional (${MK_SENDMAIL} != "no")
   "Makefile", line 8: if-less endif

Thanks for any pointers
Angelo Turetta

--------------------------------------------------------------
>>> World build completed on Sat Sep  9 13:40:17 UTC 2006
--------------------------------------------------------------
+ touch /tmp/.world_done
+ [ ! -f /tmp/.skip_ports_index ]
+ cd /usr/src/release
+ make obj
/usr/obj/usr/src/release created for /usr/src/release
+ make doRELEASE
mkdir -p /R
rm -rf /R/* 2> /dev/null
chflags -R noschg /R/.
rm -rf /R/*
mkdir /R/stage
mkdir /R/stage/trees
for i in base catpages manpages games proflibs dict info doc lib32; do  mkdir /R/stage/trees/$i &&  mtree -deU -f /usr/src/release/../etc/mtree/BSD.root.dist  -p /R/stage/trees/$i > /dev/null &&  mtree -deU -f /usr/src/release/../etc/mtree/BSD.usr.dist  -p /R/stage/trees/$i/usr > /dev/null &&  mtree -deU -f /usr/src/release/../etc/mtree/BSD.include.dist  -p /R/stage/trees/$i/usr/include > /dev/null &&  mtree -deU -f /usr/src/release/../etc/mtree/BSD.var.dist  -p /R/stage/trees/$i/var > /dev/null ;  done
mkdir /R/stage/kernels
for i in GENERIC ; do  mkdir -p /R/stage/kernels/${i};  done
touch release.1
cd /usr/src/release/../etc && make distrib-dirs DESTDIR=/R/stage/trees/base
"Makefile", line 6: Malformed conditional (${MK_SENDMAIL} != "no")
"Makefile", line 8: if-less endif
"Makefile", line 35: Malformed conditional (${MK_LPR} != "no")
"Makefile", line 37: if-less endif
"Makefile", line 39: Malformed conditional (${MK_NS_CACHING} != "no")
"Makefile", line 41: if-less endif
"Makefile", line 43: Malformed conditional (${MK_OPENSSH} != "no")
"Makefile", line 47: if-less endif
"Makefile", line 48: Malformed conditional (${MK_OPENSSL} != "no")
"Makefile", line 50: if-less endif
"Makefile", line 57: Malformed conditional (${MK_SENDMAIL} != "no")
"Makefile", line 59: if-less endif
"Makefile", line 60: Malformed conditional (${MK_BIND} != "no")
"Makefile", line 62: Malformed conditional (${MK_BIND_LIBS} != "no")
"Makefile", line 64: if-less endif
"Makefile", line 65: if-less endif
"Makefile", line 67: Malformed conditional (${MK_BIND_ETC} != "no")
"Makefile", line 70: if-less endif
"Makefile", line 74: Malformed conditional (${MK_SENDMAIL} == "no")
"Makefile", line 76: if-less else
"Makefile", line 79: if-less endif
"Makefile", line 85: Malformed conditional (${MK_MAN} != "no")
"Makefile", line 87: if-less endif
"Makefile", line 135: Malformed conditional (${MK_I4B} != "no")
"Makefile", line 137: if-less endif
"Makefile", line 138: Malformed conditional (${MK_SENDMAIL} != "no")
"Makefile", line 140: if-less endif
"Makefile", line 141: Malformed conditional (${MK_OPENSSH} != "no")
"Makefile", line 144: if-less endif
"Makefile", line 145: Malformed conditional (${MK_OPENSSL} != "no")
"Makefile", line 148: if-less endif
"Makefile", line 149: Malformed conditional (${MK_KERBEROS} != "no")
"Makefile", line 153: if-less endif
"Makefile", line 166: Malformed conditional (${MK_BIND_ETC} != "no")
"Makefile", line 169: if-less endif
"Makefile", line 170: Malformed conditional (${MK_BIND_MTREE} != "no")
"Makefile", line 175: if-less endif
"Makefile", line 203: Malformed conditional (${MK_BIND_LIBS} != "no")
"Makefile", line 206: if-less endif
"Makefile", line 207: Malformed conditional (${MK_BIND_MTREE} != "no")
"Makefile", line 210: if-less endif
"Makefile", line 211: Malformed conditional (${MK_SENDMAIL} != "no")
"Makefile", line 213: if-less endif
make: fatal errors encountered -- cannot continue
*** Error code 1

Stop in /usr/src/release.
+ umount /dev
*** Error code 1

Stop in /usr/src/release.