lusernet.app version 0.4.2-6build1 failed to build on amd64 with GCC-4.6/oneiric

lusernet.app version 0.4.2-6build1 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2461367

Details about the rebuild:
https://lists.ubuntu.com/archives/ubuntu-devel/2011-April/033042.html

Direct link to the build log: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2461367/+files/buildlog_ubuntu-natty-amd64.lusernet.app_0.4.2-6build1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 814 lines into the build log:

./obj/LuserNET.obj/MessageViewController.m.o:(.data.rel+0x28): undefined reference to `__objc_class_name_CWUUFile'
./obj/LuserNET.obj/MessageViewController.m.o:(.data.rel+0x30): undefined reference to `__objc_class_name_CWMessage'
./obj/LuserNET.obj/MessageViewController.m.o:(.data.rel+0x40): undefined reference to `__objc_class_name_CWPart'
./obj/LuserNET.obj/MessageViewController.m.o:(.data.rel+0x50): undefined reference to `__objc_class_name_CWMIMEMultipart'
./obj/LuserNET.obj/ComposeWindowController.m.o:(.data.rel+0x78): undefined reference to `__objc_class_name_CWInternetAddress'
./obj/LuserNET.obj/ComposeWindowController.m.o:(.data.rel+0x88): undefined reference to `__objc_class_name_CWMessage'
./obj/LuserNET.obj/Pref_MessageViewing.m.o:(.data.rel+0x18): undefined reference to `__objc_class_name_CWCharset'
collect2: ld returned 1 exit status
make[4]: *** [LuserNET.app/./LuserNET] Error 1
make[3]: *** [internal-app-run-compile-submake] Error 2
make[2]: *** [LuserNET.all.app.variables] Error 2
make[1]: *** [internal-all] Error 2
make[1]: Leaving directory `/build/buildd/lusernet.app-0.4.2'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110424-1326
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/lusernet.app-0.4.2