I have found a solution! At https://github.com/smirarab/sepp/blame/master/tutorial/sepp-tutorial.md#L451 they mention that you need to remove a line in my info file that read: ‘Partition: 0 with name: No Name Provided’ and this has let the script finish once I put that back in share/fragment-insertion/ref/
Thanks so much for your help - have a great day!