System.Exception: System.Data.OracleClient requires Oracle client software version 8.1.7 or greater

Solution:

go to :-
C:\Oracle\product\10.1.0\Client_2 folder

follow the below steps:
1) right click on this folder
2) go to properties
3) select "administrator"
4) remove 'Read & Executes' permission
5) again add 'Read & Executes' permission on this folder

there you go...