Custom Activity Error?

So I built an activity that works in Visual Studio but porting it to UiPath I get an assembly reference error. Not sure why it happens in UiPath. Any help would be appreciated.

Error: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.IO.FileLoadException: The located assembly’s manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
at System.Signature.GetSignature(Void* pCorSig, Int32 cCorSig, RuntimeFieldHandleInternal fieldHandle, IRuntimeMethodInfo methodHandle, RuntimeType declaringType)
at System.Reflection.RuntimeMethodInfo.FetchNonReturnParameters()
at System.Reflection.RuntimeMethodInfo.GetParametersNoCopy()
at System.Reflection.RuntimePropertyInfo.GetIndexParametersNoCopy()
at System.Reflection.RuntimePropertyInfo.GetIndexParameters()
at System.ComponentModel.ReflectTypeDescriptionProvider.ReflectGetProperties(Type type)
at System.ComponentModel.ReflectTypeDescriptionProvider.ReflectedTypeData.GetProperties()
at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.DefaultTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties()
at System.Activities.Presentation.Metadata.MetadataStore.MetadataStoreProvider.MetadataStoreTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties()
at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.DefaultTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties()
at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.DefaultTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties()
at System.Activities.Presentation.Model.ModelPropertyCollectionImpl.GetPropertyDescriptors()
at System.Activities.Presentation.Model.ModelPropertyCollectionImpl.d__3.MoveNext()
at System.Activities.Presentation.Internal.PropertyEditing.Model.ModelPropertyMerger.d__7.MoveNext()
at System.Activities.Presentation.Internal.PropertyEditing.PropertyInspector.UpdateCategories(Selection selection, Boolean attachedOnly)
at System.Activities.Presentation.Internal.PropertyEditing.PropertyInspector.RefreshPropertyList(Boolean attachedOnly)
at System.Activities.Presentation.Internal.PropertyEditing.PropertyInspector.OnSelectionChangedIdle()
— End of inner exception stack trace —
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object parameters, Object arguments)
at System.Delegate.DynamicInvokeImpl(Object args)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler), HResult -2146232828