Attribute 'messageBar' not found in tag library 'HTMLB' for the tag form.

Can anyone tell me why I get this message when I try to implement the following jsp component?

<hbj:messageBar

id="mBar"

messageType="ERROR"

messageText="Fatal Error" >

<% myFormId.setMessageBar(mBar); %>

</hbj:messageBar>

The message I'm getting is:

Attribute 'messageBar' not found in tag library 'HTMLB' for the tag form.