When you are trying to use session state mode sqlserver then you need to activate or enable the sqlserver and asp.net connectivity for session maintain in sql server.

If connectivity is not installed then you may get the error"Unable to use SQL Server because ASP.NET version 2.0 Session State is not installed on the SQL server. Please install ASP.NET Session State SQL Server version 2.0 or above."

To solve this. do the following steps:

(1) Open command prompt and go on following path.
be sure to run this in the correct directory)

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>aspnet_regsql.exe -ssadd -sstype c -d DATABASENAME -E

(2)change DATABASENAME
to the name of your database. This will begin to start the session state.