Could not load file or assembly 'Oracle.DataAccess' or one of its dependencies. An attempt was made to load a program with an incorrect format

Question

I have installed a Web app on IIS 7.0 Windows Server 2008 R2 64bit. I am referring an oracle.DataAccess.dll; When I try to access the application I get the following message: \"

Answer 1

In my case, I use VS 2010, Oracle v11 64 bits. I might to publish in 64 bit mode (Setting to "Any Cpu" mode in Web Project configuration) and I might set IIS on Production Server to 32 Bit compability to false (because the the server is 64 bit and I like to take advantage it).

Then to solve the problem "Could not load file or assembly 'Oracle.DataAccess'" (sometime appear the "Compiler Error Message: CS1705: Assembly" error):

• In the Local PC and Server is installed Oracle v11, 64 Bit.
• In all Local Dev PC I reference to Oracle.DataAccess.dll (C:\app\user\product\11.2.0\client_1\odp.net\bin\4) which is 64 bit.
• In IIS Production Server, I set 32 bit compatibility to False.
• The reference in the web project at System.Web.Mvc.dll was the version v3.0.0.1 in the local PC, however in Production is only instaled MVC version 3.0.0.0. So, the fix was locallly work with MVC 3.0.0.0 and not 3.0.0.1 and publish again on server, and it works.

Answer 2

Yeah, it is a quite annoying issue I faced sometimes. The main problem is that an web application uses wrongly 32 bit Oracle.DataAccess.dll instead of 64 bit, or in the reverse case. There are a few solutions for it.

1. Enabling 32-bit applications in the application pool if your application is 64 bit and need to run 32 bit Oracle.DataAccess.dll.

Go to the IIS and set true for "Enable 32-Bit Applications" option in Advanced Settings of an Application pool.

2. Correcting reference dll.

Reference path is supposed to be system reference path configured by Oracle Installation process. But, some cases such as installing or updating new Oracle version, the latest DLLs doesn't update old ones, or path is changed, or a reference is not updated in the web application project. Therefore, we should correct Oracle.DataAccess reference manually.

Go to the web application and remove Oracle.DataAccess reference. And add new reference for Oracle.DataAccess. It must be correct Oracle.DataAccess.dll from your oracle installation path. For example:

C:\Oracle\product\12.2.0\client_1\odp.net\bin\4\Oracle.DataAccess.dll

ODP.NET and Dependent Unmanaged DLL Mismatch To enforce the usage of Oracle.DataAccess.dll assembly with the correct version of its unmanaged DLLs, an exception is raised if Oracle.DataAccess.dll notices it has loaded a mismatched version of a dependent unmanaged DLL.

https://docs.oracle.com/cd/E11882_01/win.112/e23174/InstallODP.htm#ODPNT152

3. Easy and quick way (but not proper solution) to fix the issue is that override directly an Oracle.DataAccess.dll file copying from oracle installation path (for example: C:\Oracle\product\12.2.0\client_1\odp.net\bin\4\ ) to Bin folder of your web application.

Hope this helps you a little. Good luck.

Answer 3

In application pool ---> click Advance settings --> Enable 32 bit option

see the this image

Answer 4

I avoided registering the 11.2 Release 5 assemblies in the GAC by setting "Enable 32-bit Applications" for the application pool to true.

Answer 5

The accepted answer, published by George Netu helped to solve my problem, but I had to fiddle with some additional trifles:

Problem description:

Under C:\Windows\assembly, I found two Oracle.DataAccess items(GAC-folders?). Relict, caused by several Oracle client installations. One item showed Version 2.112.1.0 but was actually version 2.121.2.0 (visible through Properties->Version). That inconsistency was the bug.

First unhelpful attempts:

• tried to deinstall and reinstall the Oracle full client, both in versions Runtime/Administrator
• tried to redeploy the correct .dlls
• tried to copy the new installed assemblies in the GAC serveral times, as stated in the accepted answer above via command prompt (but that didn't solve the version mismatch..)
• tried to use gacutil /i ...

Final success:

I landed on the Gacutil.exe msdn page and were ultimately able to delete the items from the C:\Windows\assembly folder.

gacutil /u Oracle.DataAccess, Version=2.112.1.0, Culture="Neutral",PublicKeyToken=45e343aae32233ca
gacutil /u Oracle.DataAccess, Version=2.212.2.0, Culture="Neutral",PublicKeyToken=45e343aae3223abc
gacutil /u Oracle.Web, Version=2.112.1.0, Culture="Neutral",PublicKeyToken=45e343aae3223def

After that, i repeated the two gacutil /i ... commands and the two dlls appeared there in consistent versions.

Finally restarted the IIS, and it works..

Answer 6

You may need to enable 32-bit applications in your AppPool.

http://www.alexjamesbrown.com/development/could-not-load-file-or-assembly-chilkatdotnet2-or-one-of-its-dependencies-an-attempt-was-made-to-load-a-program-with-an-incorrect-format/