Why does the JCO client connect method fail ?

I am starting to write a WebDynpro application on WAS 6.3. I create a JCO client object using the createClient method, and specify the client, userid, password, lasnguage, server and system number (in that order). However the connect methos failes with error "could not open saprfc.ini, no such file or directory".

I was under the impression that the saprfc.ini was not needed when all parameters were specified ?

Anybody have any ideas ?

Thanks