I have "WCF Service Application" which is .net framework 4.6.1. I need to add "Interop.zkemkeeper.dll" as a reference. but when I added this as reference to the WCF service and when service stated it shows following error on the browser.

"Server Error in '/' Application.

Could not load file or assembly 'Interop.zkemkeeper' or one of its dependencies. An attempt was made to load a program with an incorrect format. 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.BadImageFormatException: Could not load file or assembly 'Interop.zkemkeeper' or one of its dependencies. An attempt was made to load a program with an incorrect format.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Assembly Load Trace: The following information can be helpful to determine why the assembly 'Interop.zkemkeeper' could not be loaded.

=== Pre-bind state information === LOG: DisplayName = Interop.zkemkeeper (Partial) WRN: Partial binding information was supplied for an assembly: WRN: Assembly Name: Interop.zkemkeeper | 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/Dushmantha/source/repos/VFTService/VFTService/ LOG: Initial PrivatePath = C:\Users\Dushmantha\source\repos\VFTService\VFTService\bin

Calling assembly : (Unknown).

LOG: This bind starts in default load context. LOG: Using application configuration file: C:\Users\Dushmantha\source\repos\VFTService\VFTService\web.config LOG: Using host configuration file: C:\Users\Dushmantha\Documents\IISExpress\config\aspnet.config LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config. LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind). LOG: Attempting download of new URL file:///C:/Users/Dushmantha/AppData/Local/Temp/Temporary ASP.NET Files/vs/224635a0/d24b75c0/Interop.zkemkeeper.DLL. LOG: Attempting download of new URL file:///C:/Users/Dushmantha/AppData/Local/Temp/Temporary ASP.NET Files/vs/224635a0/d24b75c0/Interop.zkemkeeper/Interop.zkemkeeper.DLL. LOG: Attempting download of new URL file:///C:/Users/Dushmantha/source/repos/VFTService/VFTService/bin/Interop.zkemkeeper.DLL. ERR: Failed to complete setup of assembly (hr = 0x8007000b). Probing terminated.

Stack Trace:

[BadImageFormatException: Could not load file or assembly 'Interop.zkemkeeper' or one of its dependencies. An attempt was made to load a program with an incorrect format.] System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0 System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +36 System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +152 System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +77 System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +21 System.Reflection.Assembly.Load(String assemblyString) +28 System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +38

[ConfigurationErrorsException: Could not load file or assembly 'Interop.zkemkeeper' or one of its dependencies. An attempt was made to load a program with an incorrect format.] System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +738 System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +217 System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +130 System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +170 System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +92 System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +290 System.Web.Compilation.BuildManager.ExecutePreAppStart() +157 System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +549

[HttpException (0x80004005): Could not load file or assembly 'Interop.zkemkeeper' or one of its dependencies. An attempt was made to load a program with an incorrect format.] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +10075108 System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +95 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +254"

Could you try change Platform target to x86?

1. Click Build button on the toolbar
2. Click Configuration Manager
3. Then set Plataform target to x86