While going through a training video of the Collaboration module of the SharePoint Training Kit, I happened to to have clicked "Complete Training". After which, when I tried to view the video again, its assigned action read as "Continue", so when I clicked on "Continue", it brought up a message saying "Assignment Not Available. This assignment is not available because it has been submitted as complete. You can review this assignment after it is returned by your instructor.".
So I tried to log in to the site as an instructor but i still couldn't review any assignments. I therefore went into the SQL Database, tried to study the tables in the DB, and i finally found that in the STKTrainingResult table, a record for every training module you take is entered in this table, and there was a column named "TrainingStatus" on my particular training record that needed to change from 0 to 1 the time I had clicked on "complete training", but it didn't change. I therefore changed this field manually and I was able to retake the training video successfully.
Am sure this is not the recommended workaround though.