I have Windows Vista and I ran into the same problem you are having. The following is how Curt told me to fix it:
I would like you to try the following process if you are running Windows to see if it solves your problems. (If you are running the Workout Blender on Mac let us know.) It is not difficult but please don't attempt it if you do not feel confident. Please let us know if it solves your problem with the video creation getting stuck at 80%.
You will have to re-import your videos and re-create your workouts since this resets your Workout Blender, but since it is not working now this shouldn't make much of a difference. This process is only necessary once.
1. Exit the Workout Blender, then open your Control Panels and choose "View by: Small Icons" in the upper right corner.
2. Click to open "Folder Options"
3. Click on the "View" tab at the top of the Folder Options window that opens.
4. Under "Hidden files and folders" in the list of Advanced Settings that appears, click on "Show hidden files, folders, and drives", then click "Apply" at the bottom of the window.
5. Leave the window open since you will need to reverse this process in a minute.
6. Navigate to the folder: "Your Hard Drive" > Users > "Your User Name" > AppData > Roaming and drag the folder "Cathe" into the Recycle Bin and you can close all the folders you opened.
7. Go back to the "Folder Options" window and check "Don't show hidden files, folders, or drives", click "Apply" and close the window. You can also close your Control Panels.
8. Restart your computer, then when it is done restarting launch Workout Blender and attempt to create a new video.
Please let us know your results.
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Curtis W. Kapus