This is the reply I received from E-on. I must say, they were fairly quick to reply and be helpful.

...

In fact, the problem is not linked to your new Vue 5 Infinite Installation code (which is recognized as identical to the old one by the system, since the difference is only due to the name you entered during installation) but to your Vue 5 Esprit licence: the system uses your old Vue 5 Esprit licence to allow you using your Cornucopia items both in Vue 5 Esprit and Vue 5 Infinite (if they are compatible with Vue 5 Esprit)

That is why it is important that you indicate the same Vue 5 Esprit Serial Number as you did the first time you installed Vue 5 Infinite (normally, it is simply the Serial Number you got with Vue 5 Esprit). You must have indicated a different serial when you reinstalled Vue 5 Infinite. To fix this, you just have to remove the Vue 5 Infinite.reg file from your Windows directory and relaunch Vue 5 Infinite: you will be asked your old Vue 5 Esprit serial number. Please make sure you type it correctly. If it still does not work, do not hesitate to contact me again (and please indicate the Vue 5 Esprit serial number you are using)