Last night, I struggled with the following error for a few hours:

Could not load file or assembly ‘Oracle.DataAccess, Version=2.111.7.20, Culture=neutral, PublicKeyToken=89b483f429c47342′ or one of its dependencies. The system cannot find the file specified.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.IO.FileNotFoundException: Could not load file or assembly ‘Oracle.DataAccess, Version=2.111.7.20, Culture=neutral, PublicKeyToken=89b483f429c47342′ or one of its dependencies. The system cannot find the file specified.

Development Machine Setup:
Windows 7 64 bit
Oracle 11g Release 1 (11.1.0.7.0)

Target Machine Setup:
Windows XP 32 bit
Originally Oracle 10g, now Oracle 11g (11.1.0.6.0)

After many grueling hours of searching the darkest corners of the internet, I found this post: ODP.NET & LLBLGen Pro. The author suggests using a binding redirect to fix a problem with LLBLGen Pro (but same basic error). While I am not exactly sure what is causing my problem, adding a binding redirect fixed it. The solution seems silly. I install Oracle 11g release 1 (11.1.0.7.0), which is what it is asking for and it still cannot be found.
I install Oracle 11g (11.1.0.6.0) and add the binding redirect and it works.

Here is my config:

<assemblyBinding xmlns=”urn:schemas-microsoft-com:asm.v1″>
<dependentAssembly>
<assemblyIdentity name=”Oracle.DataAccess” publicKeyToken=”89B483F429C47342″/>
<bindingRedirect oldVersion=”2.111.7.20″ newVersion=”2.111.6.0″/>
</dependentAssembly>
</assemblyBinding>

Note: Assembly redirection can work both ways. You can re-direct calls to a new version of the to an older installed version and vice-versa. You can read more about Binding Redirects on MSDN.

I hope this post can save someone a few headaches.

Database Normalization explained