http://www.microsoft.com/reader/info/tips/nolonger.MSPX
I looked it up, and I think that EBO is not an ebook file; it is some type of configuration file created by a copy of MSReader. Do you have MSReader, and was it open at the time?
If you don't, then it is very likely that Fictionwise put up the wrong file. Email them and complain.