emails received without attachment in outlook

i have win server 2003 installed on it
domain controller 2003 and exchange server 2003

anther server installed on it isa 2000 and pc wich installed on it exchange pop wich pull the emails from the hosting web and send it to the exchange server then the exchange then the outlook can view it (((so when the cleint view his mails which came from only out side the domine or the company network and have an attachments and try to open it he get this message “”” could not open one or more attachments “”
so i go and clear all rules on exchangepop and it is the same … so please send me the solution or let me know wher i can find any thisng related to my problems