We recommend you set the LicenseKey property in the main entry point of the application. For example, the LicenseKey property can be set, for C# users, in the static main function. For VB.NET users, it can be set in the constructor of the main form or in the "Sub Main" procedure. If no entry point is available, it is recommended that the LicenseKey property be set in a static constructor of a class that will be accessed systematically before any of the library's classes are instantiated or, you can simply set the LicenseKey property immediately BEFORE you instantiate a class.

System.Object
   Xceed.Validation.Licenser

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

Licenser Members
Xceed.Validation Namespace