Technically this error would happen when your PATH variable in your system does not include path to directory of Oracle Instant Client.
However, there are times, such as my case, that you are quite sure that system PATH is correctly set and everything is right. But still, the problem persist.
The solution that work for me is to copy files from Instant Client directory and put it to apache/bin folder. First, I copy all the files there, restart my PC and the problem is solved. However I dont want my apache folder to look messy so I try to remove files that are not used and it turns out that I only need two files, oci.dll and oraociei11.dll
Still, I don’t understand why setting path to Oracle home does not work?
Here is my setup :
Windows 7, 64 bit
Oracle11g, 32 bit
Code Igniter 2.0.2