Эта ошибка обычно возникает если subversion установлена без модуля WebDAV/Delta-V (HTTP/HTTPS) repo access module. Как исправить - пересобрать subversion с этим модулем.

# cd /usr/ports/devel/subversion
# make config

обязательно выбираем SERF:

[ ] BDB               Berkeley DB support
[ ] BOOK              Install the Subversion Book
[x] FREEBSD_TEMPLATE  FreeBSD Project log template
[ ] GNOME_KEYRING     Build with GNOME Keyring auth support
[ ] KDE_KWALLET       Build with KDE KWallet auth support
[ ] MAINTAINER_DEBUG  Build debug version
[ ] MOD_DAV_SVN       mod_dav_svn module for Apache 2.X
[x] P4_STYLE_MARKERS  Perforce-style conflict markers
[ ] SASL              SASL support
[x] SERF              WebDAV/Delta-V (HTTP/HTTPS) repo access module
[x] STATIC            Build static version (no shared libs)
[ ] SVNSERVE_WRAPPER  Enable svnserve wrapper (umask setter)
[ ] TEST              Run subversion test suite
[ ] TOOLS             Install several tools (svnauthz-validate and mod_d)

если subversion установлена, делаем:

# make deinstall

а потом

# make install clean