Run Oracle Client in 32-bit mode on a 64-bit machine

I found that you have to install the 32-bit Oracle client (you can download the installer from their website) even if you are running on a 64-bit machine.

In addition, during the discussions people were talking about 32-bit mode etc. This is how you can check / set that for an IIS 7 hosted application. You shouldn't need to change this but I have added here for completeness / future reference.

• Launch IIS 7 and expand the server name node.
• Click on Application Pools node and find theapplication Pool you are using.
• On the right-hand panel click Advanced Settings...
• In the pop-up box that appears check Enabled 32-Bit Applications setting which is third option from the top.

You have to change your main .exe file to run only as 32-bit. You can do this in Visual Studio - just change Platform target from "Any CPU" to "x86".

If this is not possible, use corflags.exe which forces an existing exe to be a 32-bit application.

I have been struggling with this issue for months now and finally solved it. I think all the posts are helpful, but I had one missing piece. I didn't have a Microsoft ODBC for Oracle instance setup for User DSN or System DSN. I'm working on a Windows 8 machine. So for me I had to go to the general windows search and type in ODBC and open the ODBC Data Source Administrator (32-bit). Check to see if you have a Microsoft ODBC for Oracle setup on the User DSN tab or the System DSN tab. If not click on Add and select Microsoft ODBC for Oracle. Fill out the info for your datasource you are trying to hit and click ok. Make sure to restart your computer and that is what finally worked for me. Hope this helps some of you.