When UseSOAPAdapter is true, TSOAPConnection communicates with the application server using an IAppServerSOAP interface. It then uses an internal adapter which implements the IAppServer interface for client datasets. In this case, the GetServer method returns the IAppServer interface that the internal adapter implements. 

When UseSOAPAdpater is false, TSOAPConnection uses an IAppServer interface to communicate with the application server and exposes that interface with the GetServer method. In this case, the GetSOAPServer method returns nil (Delphi) or NULL (C++). 

The recommended setting for UseSOAPAdapter is true. Unlike IAppServer, the IAppServerSOAP interface does not use the safecall calling convention. This makes it easier to marshal interface calls when the client or server is written in C++. IAppServerSOAP is not supported, however, when the application server is built using Delphi 6 (before update patch 2) or Kylix 2. If you are connecting to a server that does not support IAppServerSOAP, set UseSOAPAdapter to false. 

IAppServer 

IAppServerSOAP 

GetServer 

GetSOAPServer 

Specifying a Connection Using SOAP