I cannot reproduce the error with proper inputs (including the tutorial data) and have been unable to locate your account at https://usegalaxy.org. This does not necessarily mean that a tool issue isn't a factor - and if there is one, we'll want to fix it. If the issue turns out to be usage, we can provide direct help. This could include updating the tool help and/or tutorial to aid others in avoiding the issue.
So, would you please send in a bug report from the error dataset? Be sure to leave the inputs and outputs undeleted. In the comments, include a link to this post and any other info you would like to add. From there, we'll troubleshoot the problem through email using the bug report as a reference. All bug report data is private to our small internal team and is never made public.
Thanks! Jen, Galaxy team