The CSD licensing system works by trying to determine a unique identifier for your computer, which is then sent to our licence server. A binary file containing activation details will be returned and stored in the registry or the user's home directory. Activation is per-user as well as per-system - if a system-wide activation has been carried out then activations for individual users will happen silently in the background, otherwise each user will have to register when using the software for the first time. However activations for additional users do not count against your activation limit.
In some cases the CSD Portfolio software can be fooled into thinking the computer is different when it is not, most often because of a hardware replacement or docking a laptop into different docking stations. This can also occasionally happen when performing the registration during installation, where the elevated rights you have to install give a different unique identifier than that the standard user has, making the serial number different for the installer compared to the user and so causing the CSD software to think it is not licensed for use on that computer.
In such situations, the first course of action is to attempt to repeat online registration of the software. If this fails please contact firstname.lastname@example.org quoting your 36-character activation key and we will be happy to assist you further.