Received above error when try to run an application done by my colleague, after hours of finding and uninstall and re-installed the Oracle 10g client it was cause by the NTSF file permission. Apparently the .NET data provider are run under difference authentication. What I did to solve this was to apply the File Securities permission to all the files and folders under oracle home folder. Same issue also affecting the ASP .NET application.
Details of relate to this issue are at link below;
Lastly, reboot of PC is a must. :-)