Win2Kpro, Outlook\OfficeXP

I have some new workstations that have an intermittent problem replying to or forwarding e-mail messages. It seems that the only way to get the reply or forward to work when this happens is to close the message, highlight it in the Inbox and –then– choose reply or forward so that you are able to type text in the reply. There seems to be no rhyme or reason to this–it happens w\ both internal and external messages. Has anyone seen this before?
Thanks in advance!!
Liz