Unable to initiate authorisation using an already existing Adobe account

I need to setup Adobe Digital Editions on a new Windows PC, and I do not currently have access to my old Windows PC that had Adobe Digital Editions (ADE) running on it. The prompt, while initiating authorisation, says that using an Adobe ID will allow me to read books across multiple devices running ADE. However, when I use an Adobe ID that was used to authorise ADE on my previous Windows PC, it says that I cannot use an already existing Adobe ID that was used on a previous computer. 

Isn't this quite contradictory? I mean, if I need to transfer DRM protected items across devices, I will have to setup each device on the same Adobe ID, if am not wrong. But it is asking me to authorise my computer using a new Adobe ID? I really do not know what is going on.