Could not load file or assembly while trying to create custom configuration section in a web config

I am trying to create my own custom configuration section with following:

Code in the web.config file:

<configuration> <configSections> <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 --> <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" /> <section name="customConfigurationSection" type="CustomConfigurationSectionRepro.ConfigHandlers.CustomConfigurationSection" allowLocation="true" allowDefinition="Everywhere" /> </configSections>
<customConfigurationSection fileName="Configscustomconfig.config" />
....
....
</configuration>

Code in the custom config handler file:

namespace CustomConfigurationSectionRepro.ConfigHandlers
{ public class CustomConfigurationSection : ConfigurationSection { [ConfigurationProperty("fileName", IsRequired = false)] public string FileName { get { return (string)this["fileName"]; } set { this["fileName"] = value; } } }
}

My web app is just a standard mvc web app from the Visual Studio MCV template. When I run it under development environment with IIS Express, I keep getting the error saying.

Could not load file or assembly 'CustomConfigurationSectionRepro' or one of its dependencies. An attempt was made to load a program with an incorrect format.
=== Pre-bind state information ===
LOG: DisplayName = CustomConfigurationSectionRepro
(Partial)
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: CustomConfigurationSectionRepro | Domain ID: 2
WRN: A partial bind occurs when only part of the assembly display name is provided.
WRN: This might result in the binder loading an incorrect assembly.
WRN: It is recommended to provide a fully specified textual identity for the assembly,
WRN: that consists of the simple name, version, culture, and public key token.
WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue.
LOG: Appbase = file:///C:/Users/vtran/Documents/Visual Studio 2015/Projects/Playground/CustomConfigurationSectionRepro/
LOG: Initial PrivatePath = C:UsersvtranDocumentsVisual Studio 2015ProjectsPlaygroundCustomConfigurationSectionReprobin
Calling assembly : (Unknown).

I've been searching around but could not find the solution. The namespace and assembly name seem to be correct. The CustomConfigurationSectionRepro.dll also does exist in the bin folder.

Any help would be really appreciated.