Could not load file or assembly 'Xceed.Wpf.Toolkit

I'm developing an add-in for another application, Autodesk Revit, which is built as a separate DLL class library. I'm trying to use the Wpf Tool Kit Property grid in one of my WPF windows. The property grid displays fine in Visual studio, and intellisense works as well. But When I try to start Revit with my add-in loaded I get the following exception.

System.Windows.Markup.XamlParseException occurred
  HResult=-2146233087
  Message=Could not load file or assembly 'Xceed.Wpf.Toolkit, PublicKeyToken=3e4669d2f30244f4' or one of its dependencies. The system cannot find the file specified.
  Source=PresentationFramework
  LineNumber=133
  LinePosition=27
  StackTrace:
       at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
  InnerException: System.IO.FileNotFoundException
       HResult=-2147024894
       Message=Could not load file or assembly 'Xceed.Wpf.Toolkit, PublicKeyToken=3e4669d2f30244f4' or one of its dependencies. The system cannot find the file specified.
       Source=mscorlib
       FileName=Xceed.Wpf.Toolkit, PublicKeyToken=3e4669d2f30244f4
       FusionLog==== Pre-bind state information ===
LOG: User = GLOBAL\eric.anastas
LOG: DisplayName = Xceed.Wpf.Toolkit, PublicKeyToken=3e4669d2f30244f4
 (Partial)
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: Xceed.Wpf.Toolkit, PublicKeyToken=3e4669d2f30244f4 | Domain ID: 1
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:/Program Files/Autodesk/Revit 2014/
LOG: Initial PrivatePath = NULL
Calling assembly : PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35.
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\Program Files\Autodesk\Revit 2014\Revit.exe.Config
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\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:/Program Files/Autodesk/Revit 2014/Xceed.Wpf.Toolkit.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/Xceed.Wpf.Toolkit/Xceed.Wpf.Toolkit.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/SDA/bin/Xceed.Wpf.Toolkit.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/SDA/bin/Xceed.Wpf.Toolkit/Xceed.Wpf.Toolkit.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/Xceed.Wpf.Toolkit.EXE.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/Xceed.Wpf.Toolkit/Xceed.Wpf.Toolkit.EXE.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/SDA/bin/Xceed.Wpf.Toolkit.EXE.
LOG: Attempting download of new URL file:///C:/Program Files/Autodesk/Revit 2014/SDA/bin/Xceed.Wpf.Toolkit/Xceed.Wpf.Toolkit.EXE.

       StackTrace:
            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.Assembly.Load(AssemblyName assemblyRef)
            at System.Windows.Baml2006.Baml2006SchemaContext.ResolveAssembly(BamlAssembly bamlAssembly)
            at System.Windows.Baml2006.Baml2006SchemaContext.ResolveBamlTypeToType(BamlType bamlType)
            at System.Windows.Baml2006.Baml2006SchemaContext.ResolveBamlType(BamlType bamlType, Int16 typeId)
            at System.Windows.Baml2006.Baml2006SchemaContext.GetXamlType(Int16 typeId)
            at System.Windows.Baml2006.Baml2006Reader.Process_ElementStart()
            at System.Windows.Baml2006.Baml2006Reader.Process_OneBamlRecord()
            at System.Windows.Baml2006.Baml2006Reader.Process_BamlRecords()
            at System.Windows.Baml2006.Baml2006Reader.Read()
            at System.Windows.Markup.WpfXamlLoader.TransformNodes(XamlReader xamlReader, XamlObjectWriter xamlWriter, Boolean onlyLoadOneNode, Boolean skipJournaledProperties, Boolean shouldPassLineNumberInfo, IXamlLineInfo xamlLineInfo, IXamlLineInfoConsumer xamlLineInfoConsumer, XamlContextStack`1 stack, IStyleConnector styleConnector)
            at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
       InnerException:

Typically when I want to reference a 3rd party assembly from a Revit plug-in I simply make sure the 3rd party DLL is being copied to the same location as my plug-in DLL. I checked and Xceed.Wpf.Toolkit.dll is being copied to the directory containing my plug-in DLL.

I noticed from the log messages in the error that it's looking for the DLL in the Revit program directory. After copying Xceed.Wpf.Toolkit.dll into this directory I no longer received the error.

However, I have existing plug-in deployment tools which depend on the plug-in files being in their own isolated folder.

So, does anyone have any idea how I can get the plug-in to find the WPF Toolkit library?

Solution

So, I found a new and better solution to this question of mine from 2014.

Today I ran into the same problem where loading a WPF control from an assembly would throw an XamlParseException, except this time it was with a WPF control library assembly that I had created.

I tried moving the DLL into the same folder as the EXE, and as before this solved the problem.

After some searching, I found this question on the telerik.com forums: http://www.telerik.com/forums/xamlparseexception-could-not-load-file-or-assembly

It turns out if you simply give the control a name, by adding a x:Name attribute, this will add a reference to the control in the code-behind and for some reason resolves the issue with loading the assembly.

  <!--This causes a XamlParseException -->
  <mylib:MyCustomControl />

  <!-- This works -->
  <mylib:MyCustomControl x:Name="foobar"/>