Hey,
The way you should follow to upload a exported course on myUdutu activity is:
-Click on Choose and Upload a file button
-Click on Upload a file button, locate your course and upload it.
-Then click on the choose button from action tab to select it. After that it should browse back to the "Updating myUdutu" page. And you will see that the Course Package text box is filled with your course's name. Then you can click on Save and display button to preview the course.
I hope this helps.
Thanks,
Cagdas