Security permissions were not properly set when the Oracle client was installed on Windows with NTFS. The result of this is that content of the ORACLE_HOME directory is not visible to Authenticated Users on the machine; this causes an error while the System.Data.OracleClient is communicating with the Oracle Connectivity software from ASP.NET using Authenticated User privileges.
To fix the problem you have to give the Authenticated Users group privilege to the Oracle Home directory.
Log on to Windows as a user with Administrator privileges.
Start Window Explorer and navigate to the ORACLE_HOME folder.
Choose properties on the ORACLE_HOME folder.
Click the “Security” tab of the “Properties” window.
Click on “Authenticated Users” item in the “Name” list.
Un-check the “Read and Execute” box in the “Permissions” list under the “Allow” column.
Re-check the “Read and Execute” box under the “Allow” column.
Click the “Advanced” button and in the “Permission Entries” verify that “Authenticated Users” are listed with permission = “Read & Execute”, and Apply To = “This folder, subfolders and files”. If not, edit that line and make sure that “Apply To” drop-down box is set to “This folder, subfolders and files”. This should already be set properly but it is important that you verify it.
Click the “Ok” button until you close out all of the security properties windows. The cursor may present the hour glass for a few seconds as it applies the permissions you just changed to all subfolders and files.
Reboot, to assure that the changes have taken effect.
Try your application again.
For more info check this : http://stackoverflow.com/questions/447983/system-data-oracleclient-requires-oracle-client-software-version-8-1-7
I hope this will help to you.