How can I open this attachment?

I get this error message: Can’t create file: (file name.xls). Right-click the folder you want to create the file in, and click Properties on the shortcut menu to check your permissions for the folder.
It is just a spreadsheet and if I send it to another user, they can open it and send it back to me. It is a recurring attachment that I’ve been opening for years and suddenly I have this problem. Our IT guy is stumped.
I even tried the ridiculous instructions in the error message and that does nothing.
Thanks.