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mage2421148579
Participant
September 29, 2025
Solved

ArgumentException: An item with the same key has already been added. Key: Assembly-CSharp

  • September 29, 2025
  • 3 replies
  • 615 views

Hey buddy, I encountered the following error when using Meta XR SDK v78 in Unity and don't know how to fix it. I also encountered this issue with v77: the project was running normally just a moment ago, but after restarting the project, this error pops up. I can fix it by deleting the Library folder in the project directory, but I want to know if there are any other simpler solutions. Does anyone know how to do this?

ArgumentException: An item with the same key has already been added. Key: Assembly-CSharp
System.Collections.Generic.Dictionary`2[TKey,TValue].TryInsert (TKey key, TValue value, System.Collections.Generic.InsertionBehavior behavior) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.Collections.Generic.Dictionary`2[TKey,TValue].Add (TKey key, TValue value) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
Meta.Conduit.Editor.AssemblyWalker..ctor (System.Collections.Generic.IList`1[T] assemblies, System.Collections.Generic.IEnumerable`1[T] compilationAssemblies) (at ./Library/PackageCache/com.meta.xr.sdk.voice@78.0.0/Lib/Wit.ai/Scripts/Editor/Conduit/AssemblyWalker.cs:65)
Meta.WitAi.Windows.ConduitManifestGenerationManager..ctor () (at ./Library/PackageCache/com.meta.xr.sdk.voice@78.0.0/Lib/Wit.ai/Scripts/Editor/Utility/ConduitManifestGenerationManager.cs:69)
System.Reflection.RuntimeConstructorInfo.InternalInvoke (System.Object obj, System.Object[] parameters, System.Boolean wrapExceptions) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.RuntimeConstructorInfo.InternalInvoke (System.Object obj, System.Object[] parameters, System.Boolean wrapExceptions) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.RuntimeType.CreateInstanceMono (System.Boolean nonPublic, System.Boolean wrapExceptions) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.RuntimeType.CreateInstanceSlow (System.Boolean publicOnly, System.Boolean wrapExceptions, System.Boolean skipCheckThis, System.Boolean fillCache) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.RuntimeType.CreateInstanceDefaultCtor (System.Boolean publicOnly, System.Boolean skipCheckThis, System.Boolean fillCache, System.Boolean wrapExceptions, System.Threading.StackCrawlMark& stackMark) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.Activator.CreateInstance (System.Type type, System.Boolean nonPublic, System.Boolean wrapExceptions) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.Activator.CreateInstance (System.Type type, System.Boolean nonPublic) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
System.Activator.CreateInstance (System.Type type) (at <356d430fdcb04bbf8dc54776e1d3627f>:0)
UnityEditor.Build.BuildPipelineInterfaces.AddToListIfTypeImplementsInterface[T] (System.Type t, System.Object& o, System.Collections.Generic.List`1[T]& list) (at <2f20f957c29d4173a2fb958401c4a8bd>:0)
UnityEditor.Build.BuildPipelineInterfaces.InitializeBuildCallbacks (UnityEditor.Build.BuildPipelineInterfaces+BuildCallbacks findFlags) (at <2f20f957c29d4173a2fb958401c4a8bd>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)

 

Best answer by GATORSAURU5

Hello there!

I would recommend contacting Unity support, they should be able to help you with this error. If you go here, Unity links developers to their support team for a similar issue.  Assembly - CSharp is a DLL that Unity creates, which could be the mismatch causing you to receive this error. 

Hope this helps!

3 replies

Meta Employee
September 29, 2025

Hello there!

I would recommend contacting Unity support, they should be able to help you with this error. If you go here, Unity links developers to their support team for a similar issue.  Assembly - CSharp is a DLL that Unity creates, which could be the mismatch causing you to receive this error. 

Hope this helps!

New Participant
May 29, 2026

Hi! 

I'm experiencing the same error, using Meta XR SDK v201..

Could you please let me know how you fixed it?

I really appreciate any help you can provide!

mage2421148579
Participant
May 30, 2026

This issue is caused by a Plastic SCM error. You can refer to the link marked as the solution for details. You may try updating Plastic SCM or uninstalling it via the Package Manager. I resolved the problem by uninstalling it. Wish you all the best!   (╭ ̄3 ̄)╭♡