Outlook 2003 not opening excel attachments

I have 4 users that are having the same problem with outlook 2003. They can open attachment with all other office programs, but cannot open excel documents. When they double click the excel icon they get the message: "Outlook has blocked access to the following potentially unsafe attachments". Normally at this point you are given the option to "open" "save" or "close". But if the document is an excel document you only get the save or close option. I have already tried the level 1 security hack that i found on microsoft's website that allows access to .xls extension but no fix. Thanks in advance for any ideas.