failed to connect to oracle 9i

Hi,
I write a client using ocilib, and I try to connect to oracle 10g, it succeeds,
then I uninstall oracle 10g, and install oracle 9i, it fails all the way:
errcode 0, errmsg (null)
what can I do to solve this problem.
PS:oracle is installed in a host(XP), and ocilib client runs in another host(Linux).
thanks
