Context Values in Generic Handlers (.ASHX) and Web Services / WebMethods (.ASMX)
Knowledge Base Article
By default in .NET framework, Generic Handlers and Web Services are processed in session separate from the one created upon visiting site using the usual means (.ASPX). This article explains what it means for you as a Kentico developer and how to modify your code in order to use the main session.
.NET Generic Handlers are not to be confused with Kentico Global Event Handlers.