The command to start the application will almost always be different on each GUI. The Invoke method of Silk Test Classic expects to find the command in the constant sCmdLine, which is defined in the main window declaration of your application. You should declare as many sCmdLine variables as there are GUIs on which your application runs, beginning each declaration with the appropriate GUI specifier.
For example, the following constants specify how Silk Test Classic should start the Text Editor application on Windows and Windows Vista:
msw32 const sCmdLine = "c:\program files\<SilkTest install directory>\silktest\textedit.exe"
mswvista const sCmdLine = "{SYS_GetEnv(‘SEGUE_APPS’)}/SilkTest/demo/textedit"