Exception in Bicycle workshop application

I am newbie here, trying to complete the bicycle workshop application following the guide. After I have saved Mechanic’s hourly rate and when i try to open Order interface, i am getting the following error message.

IllegalArgumentException: Ids must be unique, duplicate id: mechanic

Any clue, what I have missed?

(sorry i have posted this as share in idea by mistake and didnt find way to modify,…

never mind, i have found the problem, the system captured a field twice and works after removing the duplicate.