Why i am getting VBScript runtime (0x800A000D) Type mismatch: 'Session' on ASP page ?

There could be two reasons: -

1. Directory under which ASP page resides is not marked as an application. In other words, its not a *virtual* directory. 

2. *Enable Session State* option is disabled either on the virtual directory level or one level up on the root website. Path to this setting is: Right click Vdir or Website -> Choose Properties -> Virtual Directory tab -> Configuration -> Options Tab.