Error message when install xde

[alex_(_dot_)_lee_(_at_)_rieter_(_dot_)_com]

I am trying to install kde on a OpenBSD 3.1 generic fresh installation.

Encountered problem which I do not know where/how to look for info. Hope
someone can give me some ideas where to look. Thanks.

This was what I did (I used the OBSD ver 3.1 CD) :-
mount /dev/cd0a /mnt
cp /mnt/ports.tar.gz /usr
tar xvzf ports.tar.gz
cd /usr/ports/x11/kde
make install

(copy message from console)
.
.
>> Checksum OK for qt-x11-2.3.2.tar.gz. (sha1)
===>  qt2-html-3.2 depends on: png - png missing...
===>  Verifying install for png in graphics/png
===>  Checking files for png-1.2.1
`/usr/ports/distfiles/libpng-1.2.1.tar.gz' is up to date.
>> Checksum mismatch for libpng-1.2.1.tar.gz. (sha1)
Make sure the Makefile and checksum file (/usr/ports/graphics/png/distinfo)
are up to date.  If you want to override this check, type
"make NO_CHECKSUM=Yes [other args]".
*** Error code 1

Stop in /usr/ports/graphics/png (line 1496 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/graphics/png (line 1565 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/x11/qt2 (line 1296 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/x11/qt2 (line 1565 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/x11/kde/libs2 (line 1296 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/x11/kde/libs2 (line 1565 of
/usr/ports/infrastructure/mk/bsd.port.mk).
*** Error code 1

Stop in /usr/ports/x11/kde.
.
.
.

Alex Lee