Cannot add attachment on a form

[CK]

I have created an attachment field and corresponding control on a form. It
seems to work fine, but on one of my colleague's computers, he is not able to
add attachements. When he clicks on the paperclip, the manage attachment box
appears but the add and remove buttons are greyed out. He is able to view
attachments Ok. When I went into the the table, he was able to add/remove
attachments OK. So it seems that it is just a problem specific to the form
and on his PC. Any idea what might be wrong?

Thanks