Sylk file format error
I ran into this error while trying to review menus in Microsoft Excel that I had extracted from a customer's test system using SSMT. According to this article on Microsoft's support website  the issue is that the first two characters of the file I was trying to open contain the following characters "I" and "D". Sure enough, the first column was labeled "IDString".
The workaround for this problem is to open the file in a text editor and place an apostrophe character before the "I" and "D".