ipa-adtrust-install fails with error Insufficient access (50)

Issue

The AD trust install command fails create sidgen task, debug logs shows the add operation failed with "Insufficient access(50)".

    # ipa-adtrust-install
    .......
    adding new entry "cn=ipa-sidgen-task,cn=plugins,cn=config"

    2013-08-19T12:57:47Z DEBUG stderr=ldap_initialize( ldapi://%2Fvar%2Frun%2Fslapd-XXX-EXAMPLE-COM.socket/??base )
    SASL/GSSAPI authentication started
    SASL username: admin@XXX.EXAMPLE.COM
    SASL SSF: 56
    SASL data security layer installed.
    ldap_add: Insufficient access (50)
        additional info: Insufficient 'add' privilege to add the entry 'cn=plugins,cn=config'.
    adding new entry "cn=ipa_extdom_extop,cn=plugins,cn=config"

    2013-08-19T12:57:48Z DEBUG stderr=ldap_initialize( ldapi://%2Fvar%2Frun%2Fslapd-XXX-EXAMPLE-COM.socket/??base )
    SASL/GSSAPI authentication started
    SASL username: admin@XXX.EXAMPLE.COM
    SASL SSF: 56
    SASL data security layer installed.
    ldap_add: Insufficient access (50)
        additional info: Insufficient 'add' privilege to add the entry 'cn=plugins,cn=config'.

• Directory sever logs:

  [19/Aug/2013:18:27:47 +051800] conn=564 fd=72 slot=72 connection from local to /var/run/slapd-XXX-EXAMPLE-COM.socket
  [19/Aug/2013:18:27:47 +051800] conn=564 op=0 BIND dn="" method=sasl version=3 mech=GSSAPI
  [19/Aug/2013:18:27:47 +051800] conn=564 op=0 RESULT err=14 tag=97 nentries=0 etime=0, SASL bind in progress
  [19/Aug/2013:18:27:47 +051800] conn=564 op=1 BIND dn="" method=sasl version=3 mech=GSSAPI
  [19/Aug/2013:18:27:47 +051800] conn=564 op=1 RESULT err=14 tag=97 nentries=0 etime=0, SASL bind in progress
  [19/Aug/2013:18:27:47 +051800] conn=564 op=2 BIND dn="" method=sasl version=3 mech=GSSAPI
  [19/Aug/2013:18:27:47 +051800] conn=564 op=2 RESULT err=0 tag=97 nentries=0 etime=0 dn="uid=admin,cn=users,cn=accounts,dc=xxx,dc=example,dc=com"
  [19/Aug/2013:18:27:47 +051800] conn=564 op=3 ADD dn="cn=IPA SIDGEN,cn=plugins,cn=config"
  [19/Aug/2013:18:27:47 +051800] conn=564 op=3 RESULT err=50 tag=105 nentries=0 etime=0
  [19/Aug/2013:18:27:47 +051800] conn=564 op=4 UNBIND