giflib update failed 4.1.6 -> 4.2.0_1

[n dhert]

during my weekly portupgrades, giflib update failed:
...
...
Making all in doc^M
xmlto xhtml-nochunks gif2rgb.xml^M
xmlto: /usr/ports/graphics/giflib/work/giflib-4.2.0/doc/gif2rgb.xml does
not val
idate (status 3)^M
xmlto: Fix document syntax or use --skip-validation option^M
I/O error : Attempt to load network entity
http://www.oasis-open.org/docbook/xml
/4.1.2/docbookx.dtd^M
/usr/ports/graphics/giflib/work/giflib-4.2.0/doc/gif2rgb.xml:4: warning:
failed
to load external entity "
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dt
d"^M
   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>^M
                                                                 ^^M
I/O error : Attempt to load network entity
http://www.oasis-open.org/docbook/xml
4.1.2/docbookx.dtd^M
warning: failed to load external entity "
http://www.oasis-open.org/docbook/xml/4
.1.2/docbookx.dtd"^M
validity error : Could not load the external subset "
http://www.oasis-open.org/d
ocbook/xml/4.1.2/docbookx.dtd"^M
Document /usr/ports/graphics/giflib/work/giflib-4.2.0/doc/gif2rgb.xml does
not v
alidate^M
*** Error code 13^M
^M
Stop in /usr/ports/graphics/giflib/work/giflib-4.2.0/doc.^M
*** Error code 1^M
^M
Stop in /usr/ports/graphics/giflib/work/giflib-4.2.0.^M
*** Error code 1^M
^M
Stop in /usr/ports/graphics/giflib/work/giflib-4.2.0.^M
*** Error code 1^M
^M
Stop in /usr/ports/graphics/giflib.^M
--->  Build of graphics/giflib ended at: Mon, 04 Jun 2012 09:43:14 +0200
(consum
ed 00:03:57)
--->  Upgrade of graphics/giflib ended at: Mon, 04 Jun 2012 09:43:14 +0200
(cons
umed 00:03:57)
--->  ** Upgrade tasks 49: 6 done, 0 ignored, 0 skipped and 1 failed
What's wrong and how to solve ?