Is this for a or reactivation after a system change? Once I know this, I can tell you exactly how to fix it. Radmin Support Center
Unlike many modern remote desktop tools (like TeamViewer) that use subscription models, Radmin uses a perpetual license [30]. Once you buy a serial key, it does not expire for that version. License Scope: Serial Key Radmin 3.5
Radmin 3.x utilizes a "per-server" licensing model, meaning you must purchase one license for every remote computer you intend to control. Is this for a or reactivation after a system change