Why do I get "Could not load file or assembly EasyXLS" error?

The following error might occur at runtime when using EasyXLS Excel library:

Could not load file or assembly 'EasyXLS, Version=8.6.0.0, Culture=neutral, PublicKeyToken=632c31013494909a' or one of its dependencies. An attempt was made to load a program with an incorrect format.

Possible reason #1: Windows 64-bit, Visual Studio project and EasyXLS.dll for 32-bit

If the EasyXLS version for 32-bit is used on a Windows 64-bit operating system, check the project properties and make sure that the target machine is set to x86.

Possible reason #2: Visual Studio project and EasyXLS.dll for 64-bit

If the EasyXLS version for 64-bit is used, check the project properties and make sure that the target machine is set to x64 or Any CPU for a Windows 64-bit operating system.

EasyXLS.dll for 64-bit cannot run on Windows 32-bit operating system. EasyXLS.dll for 32-bit must be used at runtime.

Possible reason #3: Windows 64-bit, IIS Server (web application) and EasyXLS.dll for 64-bit

If the EasyXLS version for 64-bit is used on a Windows 64-bit operating system, make sure that IIS allows running of 64-bit applications.

Open Internet Information Services (IIS) Manager on Control Panel/Administrative Tools. Select Application Pools and the application pool associated with your web application.



Select Advanced Settings and check if Enable 32-bit Application option is set to false.



If running from Visual Studio environment, be sure that the application pool and platform target settings are matching (see Possible reason #1 and Possible reason #2 for details).

Possible reason #4: Windows 64-bit, IIS Server (web application) and EasyXLS.dll for 32-bit

If the EasyXLS version for 32-bit is used on a Windows 64-bit operating system, make sure that IIS allows running of 32-bit applications.

Open Internet Information Services (IIS) Manager on Control Panel/Administrative Tools. Select Application Pools and the application pool associated with your web application.



Select Advanced Settings and check if Enable 32-bit Application option is set to true.



If running from Visual Studio environment, be sure that the application pool and platform target settings are matching (see Possible reason #1 and Possible reason #2 for details).

Possible reason #5: Visual Studio Development Server (web application) and EasyXLS.dll for 64-bit

If the EasyXLS version for 64-bit is used in a web application that uses Visual Studio Development Server as web server, the error occurs because Visual Studio Development Server always run on 32-bit.

Possible solutions are:

I) Use EasyXLS.dll 32-bit

II) Go to project properties, Web tab and check "Use Local IIS Web server" and configure IIS server to support 64-bit applications (see Possible reason #3).

Possible reason #6: Visual Studio, IIS Express (web application) and EasyXLS.dll for 64-bit

If the EasyXLS version for 64-bit is used in a web application that uses IIS Express as web server, the error occurs because IIS Express runs on 32-bit by default.

To check if Visual Studio is using IIS Express to run your web page, go to project properties, Web tab and check Servers section:



Possible solutions are:

1. Go to Tools, Options, Projects and Solutions, Web Projects and check "Use the 64 bit version of IIS Express" (for Visual Studio 2013 or later)
2. Use EasyXLS.dll 32-bit
3. Go to project properties, Web tab, check "Use Local IIS Web server" and configure IIS server to support 64-bit applications (see Possible reason #3).
4. Go to project properties, Web tab and unselect the checkbox "Use IIS Express"
5. Run the 64-bit IIS Express by executing the following command manually:

"C:\Program Files\IIS Express\iisexpress.exe" /config:"U:\IISExpress\config\applicationhost.config" /site:"YourSite.Web" /apppool:"Clr4IntegratedAppPool"

Open Project properties, select "Web" tab, "Use Custom Web Server", and enter the URL to your site.

In order to Debug, go to debug > Attach to Process... and then select your running IIS Express instance.

Possible reason #7: Publishing a web site project in Visual Studio

When publishing a web site project type, Visual Studio uses AnyCPU as platform target by default if "Precompile during publishing" option is used:



This behavior can be changed by updating "website.publishproj" file, "Platform" tag:

<Platform Condition=" '$(Platform)' == '' ">x64</Platform>    for EasyXLS.dll 64bit
or
<Platform Condition=" '$(Platform)' == '' ">x86</Platform>    for EasyXLS.dll 32bit

Contact us for any other reasons

If none of the above, contact us at support@easyxls.com with details about your application configuration and the full error message.