I would start by looking at the contents of that file with a text editor, see if there is any XML in it. (Note: you may need to convert the file from a Zip package before you can do that, or use a Mac and BBEdit (which can read "into" Zipped formats like ePub and XSLX and show the plain-text contents therein). The Excel-reading gems that I know of only work on "modern" Excel, the XML-based formats. I've not heard of this XSLB format before, could it mean that it's a binary file? You should know when you look in the package. If it does turn out to be that, you may need to use something like OpenOffice or a Windows server and COM objects to deal with it.