ASP.NET IMPERSONATION AND ORACLE 8.1.7

i'm trying to connect to oracle 8.1.7 in asp.net using windows integrated
security
but i'm always getting a ora 01017 invalid username/password. logon denied
message. my web application is running on iis on windows xp professional.
this is my connection string
This is my connection string: data Source=bankiby;integrated security=yes"

The strange this is that it WORKS if I explicitly set
<identity impersonate="true" userName="IISGroup\userName"
password="password" /> in the web.config file. but it doesn' t work when I
just set impersonate=true.. I want it to work by just setting
impersonate=true.


ANY SUGGESTIONS?



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