Gotham is still in the first stage of beta testing and not everything from 'classic ASP' will work. Having said that the list that does not work is quite small. This list includes

Global.asa

Currently only the Application_OnStart and Session_OnStart events will fire

Classes

You cannot use your own ASP classes in Gotham. The syntax will be parsed but no code generated for them. This will be supported in the near future.

External Objects

External objects other than ADO and the FileSystemObject set of objects. This refers to the objects you create via CreateObject or Server.CreateObject. These functions create external COM objects that ASP can talk to. In ASP you cannot just create an object and talk to it, you need to know lots about it first. There is a framework built into Gotham to allow this object creation to be set-up -- it has not been fully completed yet

Nested With Statements

These are not currently supported. We may support this in future. If you code contains nested With statements you should consider rewriting them -- they are very inefficient.