If you developed .Net Applications with Oracle Backend,you may face this problem if you installed Oracle Client Version 9.1.x or greater,when you try to connect to Oracle DB you will get this error :
"System.Data.OracleClient Requires Oracle Client version 8.1.7 or greater"
simply it is not a code problem,it is a securtiy issue,to fix it simply do the following :
1- Go to the Oracle Client folder.
2- Right Click on the folder.
3- On security Tab, Add "Aithenticated Users" and give this account Read & Execute permission.
4- Apply these security for all folders,Subfolders and Files (IMPORTANT).
5- DON't Forget to REBOOT your Machine,if you forgot to do this you will still face the same problem unless you restart your machine.
Happy .Netting with Oracle.