We had a thread on BHO on this which some members claimed they had difficulty. From my own experience as I also only joined last week it rejected my VIN number twice as being invalid (it wasn't) but accepted it the following day at the first attempt.
Make sure you follow the instructions correctly at the bottom of the page after you have filled all the details in for them to accept it. It's the part which states "Select this link to add your bike details' You have to select that and it refreshes your VIN and bike model which you have already previously entered, back into the window below it. If it doesn't do that you will fail.
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Ride on !
