I recently had a client who experienced an Activation error while trying to request a license file. The error received told him that Reactivation was required, even though he had not tried to activate it before. Although this type of scenario can be annoying, it can be resolved pretty easily.
If you experience this error you can contact your reseller or you can contact Autodesk directly. In either case, the activation must be handled manually by calling Autodesk and giving them the required Host Name and Host ID, product serial number and company information. they will then generate the license file and email it to the contact email address you supply to them.