Error when adding workflow XAMLX files to Visual Studio proj

After downloading the Sitefinity Resources zip for workflow files from GitHub here:

github.com/.../master.zip

 I get an error when trying to add the workflow files to my project:

 "Activity could not be loaded because of errors in the XAML"

 I am running Sitefinity 6.1. I am not sure if I should be downloading the workflow files from somewhere else or is there a problem with my project?

 Attached is a screenshot of the error in Visual Studio.

Hello Tom,

A possible reason for this error might be if you have modified the Activity file after adding it to the Workflow file. Please note that the XAML is not automatically updated when the activity is changed and this results in invalid XAML code. Please take a look here: http://stackoverflow.com/questions/10553229/activity-could-not-be-loaded-because-of-errors-in-the-xaml.

In addition, you can download the default workflow files for Sitefinity 6.1 from your SDK installation folder/Content/Resources. 

You can find more details on how you can extend the built-in workflow process in the following documentation article. You may also check out the following video demonstrations:

1. Sitefinity Custom Workflows - Part 1
2. Sitefinity Custom Workflows - Part 2