This is happening due to a configuration problem on the sender’s end with the way their client is configured to Encode attachments. Chances are they are using a version of outlook and you are not using outlook.
This often occurs when they are using stationary, or some cheesy Outlook formatting thing.
If you happen to be a network administrator of the person actually sending the attachment here is a article that may help you from Microsoft.
If all else fails, here is a utility that will help you to endure the problem… but it’s generally on the sender’s end that this needs to be resolved.