Server Error in '/' Application.
Unable to serialize the session state. In 'StateServer' and 'SQLServer' mode, ASP.NET will serialize the session state objects, and as a result non-serializable objects or MarshalByRef objects are not permitted. The same restriction applies if similar serialization is done by the custom session state store in 'Custom' mode.Description:An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.
Microsoft .NET Framework Version:2.0.50727.5448; ASP.
The exception is self explanatory. As per the exception you are using Table class to store in Session and session mode might be either StateServer or SQLServer. In both session modes we have to use only serializable class to store in session. Serializable class means class marked/decorated with Serilizable attribute.
You can not use Asp.net Table in Session as it is not a serializable class. Create your own custom class and mark it with Serializable attribute and store it in session.
and Check your configuration settings to set session state Some thing like InProc, SqlServer etc...