Concerning extracting of the files I am able with success to extract the files tough using 7zip archiver might encounter an issue, if possible use winzip or the built in extractor in windows. I have zipped myself the workflow and you can download the archive attached to the ticket as additonal attempt to get the workflows, refer to the attached Workflows.zip.
The error can be caused if opening the .xaml file from website project if you are running sitefinity as asp.net website. Open the .xamlx file from a project(class library or sitefinity as web application project) to render the .xaml. If you are using sitefinity workflows that are distributed with sitefinity SDK they are the same as the one embedded into sitefinity assemblies and contain no errors.