can't build virtualbox-ose

[felix]

hi,all
     when i build the port, it shows the following messages.
===>  Installing for gnutls-2.12.23_1
===>   Generating temporary packing list
===>  Checking if security/gnutls already installed
===>   gnutls-2.12.23_1 is already installed
       You may wish to ``make deinstall'' and install this port again
       by ``make reinstall'' to upgrade it properly.
       If you really wish to overwrite the old port of security/gnutls
       without deleting it first, set the variable "FORCE_PKG_REGISTER"
       in your environment or the "make install" command line.
*** [check-already-installed] Error code 1

Stop in /usr/ports/security/gnutls.
*** [install] Error code 1

Stop in /usr/ports/security/gnutls.
*** [lib-depends] Error code 1

Stop in /usr/ports/devel/gsoap.
*** [install] Error code 1

Stop in /usr/ports/devel/gsoap.
*** [build-depends] Error code 1

Stop in /usr/ports/emulators/virtualbox-ose.
*** [install] Error code 1

Stop in /usr/ports/emulators/virtualbox-ose.

I had run "portupgrade -fr security/gnutls", even though i run 
"portupgrade -a", the problem is still.
any hints?
thanks

felix

-- 
FreeBSD FreeBSD 9.1-RELEASE-p5 #0: Sat Jul 27 01:14:23 UTC 2013     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64