Just to check, has the PIN been entered for the dentist in 'Main Menu\Users' on the second tab called '2006 Contract'? If it hasn't been, it needs to be entered there and then in future you will just need to enter it when you wish to carry out an EDI\Send & Receive.
If you need any further clarification or information then do please get back to me.
I hope this resolves your query.
Try clicking the 'Log In' button on the EDI Send & Receive screen without entering anything in the 'Enter PIN' box and let me know if a tick appears next to her name.
In that case a PIN has been entered on the User Tab but it obviously does not match the number you are now trying to enter, which is why it keeps coming up with the error message. Unfortunately it sounds as if this PIN was either entered incorrectly or has now become corrupted.
This matter will have to be dealt with by the support desk as they will have to work their magic in order to ensure that the PIN is set correctly.