not referenced in an OBJECT-GROUP??

[CK Ng]

Hi,
Can anyone give me a clue what's wrong with the below mib??
tq.

- ck ng

ERROR: (by AgentGen)
======
A-MIB: aData is not referenced in an OBJECT-GROUP or a NOTIFICATION-GROUP
definition


THE MIB
=======

A-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY,
    OBJECT-TYPE,
    experimental        FROM SNMPv2-SMI

aMib MODULE-IDENTITY

    LAST-UPDATED "0006021600Z"

    ORGANIZATION "xxx"

    CONTACT-INFO
            "        xxx
             Postal: xxx
             E-mail: xxx"

    DESCRIPTION
            "The MIB module for entities implementing the
            xxx protocol."

    REVISION      "0006021600Z"

    DESCRIPTION
            "The initial version of this MIB module."

    ::= { experimental xx }

    aData OBJECT-TYPE
            SYNTAX      OCTET STRING (SIZE(0..255))
            MAX-ACCESS  read-write
            STATUS      current
            DESCRIPTION
                    "The data for display."
    ::= { aMib 1 }
END