Today I have tried to connect to Oracle database using Business Connectivity Service (BCS) to crawl the data in the database so the end user can able to search this data but I got the following  error when try to Crawl the content source :

The error in SharePoint Log:

Errorinfo is "System.Data.OracleClient requires Oracle client software version 8.1.7 or greater."

I have installed Oracle Client 11g (11.2.0.1.0) on Search Servers (Index Servers) which is greater than 8.1.7 so as Mr. Moustafa arafa said in his post

http://moustafa-arafa.blogspot.com/2007/04/systemdataoracleclient-requires-oracle.html

It is a security issue, so to fix it simply do the following:

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.