Error System.Data.OracleClient requires Oracle client software version 8.1.7 or greater when installs setup

It is a security issue, so 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 "Authenticated Users" and give this account Read & Execute permission.
4. Apply this 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.

http://blogs.msdn.com/b/fabdulwahab/archive/2011/11/13/system-data-oracleclient-requires-oracle-client-software-version-8-1-7-or-greater.aspx

The error message is pretty self-explanatory: your application needs the Oracle Client installed on the machine it's running on. Your development PC already has it. Make sure your target PC has it, too.

Edit: The System.Data.OracleClient namespace is deprecated. Make sure you use the driver native to your database system, that would be ODP.NET from Oracle.