Forum OpenACS Q&A: xowiki::Form error on new 5.8.1 install

I just installed 5.8.1 on a fresh Debian Wheezy using the install-ns.sh and install-oacs.sh, both of which worked beautifully. Installing xowiki from the OpenACS repository gives xowiki-0.156. However, going to the instance gives this error:

invalid command name "::xowiki::Form"
    ::ns_cache->eval
    invoked from within
"ns_cache eval xotcl_object_type_cache root_folder-$id {
      
      set folder_id [::xo::db::CrClass lookup -name $name -parent_id $parent_id]
      ..."
    (procedure "require_root_folder" line 4)
    ::1033 ::xowiki::Package->require_root_folder
    invoked from within
"my require_root_folder -name "xowiki: [my id]"  -content_types ::xowiki::Page* "
    (procedure "require_folder_object" line 2)
    ::1033 ::xowiki::Package->require_folder_object
    invoked from within
"my require_folder_object"
    (procedure "init" line 4)
    ::1033 ::xowiki::Package->init
    ::1033 ::xotcl::Object->residualargs
    ::xowiki::Package ::xotcl::Class->create
    invoked from within
"$package_class create ::$package_id -destroy_on_cleanup -id $package_id -url $url"
    (procedure "require" line 31)
    ::xowiki::Package ::xo::PackageMgr->require
    invoked from within
"my require -url $url $package_id"
    (procedure "initialize" line 34)
    ::xowiki::Package ::xo::PackageMgr->initialize
    invoked from within
"::xowiki::Package initialize -ad_doc {
....