DisplayNote is different to most other software as you don't actually need a license key to install the software on a device. Instead the license key is used to create a Presenter account on our website.
Each license is only allowed to be used a set number of times. If you receive the message "This license has reached its activations limit, please contact support", then your license has reached this limit.
If you just need to download and install DisplayNote again, you can do this from the download page.
If you still need to contact support, you can do so here.