Forum OpenACS Q&A: Error installing Forums with OpenACS4.6

Hi all,
I'm having troubles installing the forums package on my freshly installed OpenACS 4.6 running on PostgreSQL 7.1.

The error is:

psql:forums-forums-create.sql:27: ERROR:  triggered data change violation on relation "acs_privilege_hierarchy_index"

    invoked from within
"db_source_sql_file -callback $callback $path/$file_path"
    (procedure "apm_package_install_data_model" line 32)
    invoked from within
"apm_package_install_data_model -callback $callback -data_model_files $data_model_files $spec_file_path"
    (procedure "apm_package_install" line 19)
    invoked from within
"apm_package_install -install_path $install_path  -callback apm_ns_write_callback -load_data_model  -data_model_files $data_model_files $spec_file"
    ("foreach" body line 36)
    invoked from within
"foreach pkg_info $pkg_install_list {
    set spec_file [pkg_info_spec $pkg_info]
    if { [catch {
	array set version [apm_read_package_info_file $spe..."
    ("uplevel" body line 34)
    invoked from within
"uplevel {
    	  ad_page_contract {

I got this on the browser before the error:

 acs_privilege__add_child 
--------------------------
                        0
(1 row)
*ABORT STATE*
*ABORT STATE*
*ABORT STATE*
*ABORT STATE*
*ABORT STATE*
*ABORT STATE*
*ABORT STATE*
COMMIT
CREATE
CREATE
CREATE
 inline_0 
----------

and it seems that the error is caused by the second execution of the function acs_privilege__add_child.

Any ideas?