I did a QuickBooks data file repair last week. The error on that data file was "Duplicate Element".
Usually, duplicate element error will appeared during verify data process. When error occurred, QuickBooks program will be aborted by itself.
Duplicate element error was due to duplicated names in the list item. It could be in your Customer:job list, Supplier name list, Other name list, Employee name list, Item list or even in the Customer Message list.
In most of the cases, just check which list having the duplicate element and delete off the duplicate name from the list will resolve the issue.
The most difficult list to resolve is Customer Message list. This is because you cannot have a preview on where this name was being used in your transactions.
Last time I had a case that this user used the Customer Message as the exchange rate of the invoice. So she had hundreds of Customer Messages in the list. To resolve it, you have to check your transactions one-by-one and edit them accordingly. It was a painful exercise to be done.
I suggest you keep the Customer Message list simple. Just use it for standard message such as "Thank you for your business", or some important messages from your company.
You can join my training to learn a proper way of using QuickBooks.