Session variable works fine with InProc Session Mode but is null when you switch the Session Mode to SQLServer mode.
You may see the following exception. "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." Make sure you check the inner exception to see which class needs to be changed to Serializable.
Review all the data you have stored in Session variables to verify the data is serializable. .NET knows how to automatically serialize the simple built in types like string, enum, integer, etc. Any classes you create are NOT serializable by default. Fortunately, you can make your classes serializable with a simple class attribute of [Serializable] like this.
public class Address
public int nStreetNum;
public string strStreetName;
public class Customer
public string strFirstName;
public string strLastName;
public Address Addr; // The Address class must be serializable.
RadWindowManager in User Control Can Cause Confusion
I had a RadWindowManager in a user control that was loaded dynamically in an aspx page which also had it's own RadWindowManager. So now there are two RadWindowManagers on the page after the user control was loaded.
The following comes from a post at a Telerik forum:
the radopen() function can be used only when a RadWindowManager is declared on the page.
If there are multiple RadWindowManagers on the page, radopen() will use the first rendered manager.