WiX Custom Action Error - An attempt was made to load a program with an incorrect format

[MattWalker414]

I've rewritten some custom actions with WiX v4.0.3 and I've run up against an issue. The install fails with....

Action start 9:37:25: MyCustomAction.
MSI (c) (8C:60) [09:37:25:273]: Invoking remote custom action. DLL: C:\Users\BUILDU1\AppData\Local\Temp\MSI7E87.tmp, Entrypoint: MyPlugIn
SFXCA: Extracting custom action to temporary directory: C:\Users\BUILDU1\AppData\Local\Temp\MSI7E87.tmp-
SFXCA: Binding to CLR version v4.0.30319
Calling custom action MyCustomAction!MyCustomAction.CustomActions.MyPlugIn
Error: could not load custom action class MyCustomAction.CustomActions from assembly: MyCustomAction
System.BadImageFormatException: Could not load file or assembly 'MyCustomAction' or one of its dependencies. An attempt was made to load a program with an incorrect format.
File name: 'MyCustomAction'
at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection)
at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection)
at System.AppDomain.Load(String assemblyString)
at WixToolset.Dtf.WindowsInstaller.CustomActionProxy.GetCustomActionMethod(Session session, String assemblyName, String className, String methodName)

WRN: Assembly binding logging is turned OFF.
To enable assembly bind failure logging, set the registry value (DWORD) to 1.
Note: There is some performance penalty associated with assembly bind failure logging.
To turn this feature off, remove the registry value .

CustomAction MyCustomAction returned actual error code 1603 (note this may not be 100% accurate if translation happened inside sandbox)
Action ended 9:37:25: MyCustomAction. Return value 3.
MSI (c) (8C:8C) [09:37:25:606]: Doing action: SetupCompleteError

I'm not sure what I might be missing. Any help appreciated!

[MattWalker414]

I figured out my problem. I have Post-Build steps set up to recreate the *.CA.dll because a typical compile through Visual Studio would not have the encapsulated .dll digitally signed. So when I recreate the .CA.dll...

"%25HOMEPATH%25.nuget\packages\WixToolset.Dtf.CustomAction\4.0.3\tools\WixToolset.Dtf.MakeSfxCA.exe" "$(TargetDir)$(TargetName).CA.dll" "%25HOMEPATH%25.nuget\Packages\WixToolset.Dtf.CustomAction\4.0.3\tools**x64**\SfxCA.dll" "$(TargetPath)" "$(TargetDir)CustomAction.config" "$(TargetDir)WixToolset.Dtf.WindowsInstaller.dll"

,... I was pointing to the x86 SfxCA.dll for my 64 bit actions. That caused the issue.