When asking for assitance in this forum, or any other forum, it helps if you include the application you are working with and some specific details related to the problem you are having.
Telling us that you have a "certain attachment" that won't open doesn't give us a lot to work with.
What application are you trying to open the attachment from?
What is the filetype of the attachment?
What happens when you try to open it? Nothing? An error? A message?
Providing details such as these - in your first post - helps us help you more efficiently.