I am running Apache 1.3.20 with PHP 4.0.6 under Windows 2000. I've got exactly the same error message as you and can't manage to make it working.
I've read in some forums that using simultaneously the oci8 AND oracle libs may conflicts and that you should use one OR another and not both otherwise you would get our error message !
It might work for you, but for me this hasn't change a thing to remove the oracle (ORA) extension.
I think this comes from Oracle rather than PHP. Must we install an Oracle client for the OCI.dll lib to work, even if a server is already installed ? In this case, are the 2 OCI.dll files different ?
please HELP !