Hi Victor,
Thanks for letting me know, that is strange, somewhere along the way the part of the post build event that copies that file must have been lost. I've fixed it in the source code repository so it will be included in the next release.
For now, anyone can restore that file by creating a text file named BlogSiteMap.ashx in the /Blog folder with the following content:
<%@ WebHandler Language="C#" CodeBehind="BlogSiteMap.ashx.cs" Class="mojoPortal.Web.BlogSiteMap" %>
Best,
Joe