Error "The tracking number is already in use for this order."

[RichInventions]

I have a brand new order that I have yet to dispatch, ordered brand new postage from Royal Mail, have a brand new tracking code that's never been used, however when I select tomorrow for dispatch, include my usual message, and add the tracking reference, I get this error; "The tracking number is already in use for this order.". 

The only thing I have changed recently is the name of the shop and removed many items for sale - would that make a difference?

Any ideas?

cheers

Richard

[RichInventions · Accepted solution]

Sorry, I was going to delete this but there isn't an option. I went to my completed orders and it is already there. The only thing I can think of is that I must have double-clicked when marking as complete. Either that or I am losing the plot!