One possible cause of this is that the Organizer IIS application is configured for ASP.NET 2.0 rather than ASP.NET 1.1.
To resolve this, right click on the Organizer virtual directory in the IIS Admin tool and select Properties. If you have an ASP.NET tab, select it. You will see a drop down list containing ASP.NET 2.0 and ASP.NET 1.1. If ASP.NET 2.0 is selected then this will explain the problem. Select ASP.NET 1.1, restart IIS (by issuing the command iisreset /restart from a command prompt) and then log back in into Softalk Organizer.