Cannot open any emails that have a digital signature.

[Warner]

i cannot open any email with the digital signature in Outlook. i can open
them in Outlook Express, but the email body is empty.

here is the circumstance:

1. i am using Exchange account and i am on the client side.(not the Exchange
server)

2. The version of Outlook is Outlook 2000 (CW).

3. the size of email is about 4kb.

can anybody give me advise? please help me, thanks a lot!