Asp.Net Session is null in ashx file
You have to "implement" either IRequiresSessionState or IReadOnlySessionState, with former providing full access to session, and the latter providing read-only access.
I'm quoting "implement" here because these two are so-called "marker interfaces", which means they have no members.
In VB, implement the interfaces mentioned by Anton (IRequiresSessionState or IReadOnlySessionState) like this:
Public Class MyAshxFile Implements System.Web.IHttpHandler Implements System.Web.SessionState.IRequiresSessionState ''need this for session variables Implements System.Web.SessionState.IReadOnlySessionState ''need this for session variables