Lost work

Somehow in the midst of using Visual InterDev to manage my project files and XMLSpy to edit my XML/XSL files, I lost a day and a half of work yesterday. The file went from 5K of XSL to...an empty file. Pleased I am not. Fortunately I was able to re-create it fairly quickly using Friday's version as a starting point (everything is kept in SourceSafe), but I could have done many other things with that afternoon.