diff --git a/Modules/US/USHardwareTelemed/mitkUSTelemedScanConverterPlugin.cpp b/Modules/US/USHardwareTelemed/mitkUSTelemedScanConverterPlugin.cpp
index a3a3c67dda..fb7b688b67 100644
--- a/Modules/US/USHardwareTelemed/mitkUSTelemedScanConverterPlugin.cpp
+++ b/Modules/US/USHardwareTelemed/mitkUSTelemedScanConverterPlugin.cpp
@@ -1,148 +1,149 @@
 /*===================================================================
 
 The Medical Imaging Interaction Toolkit (MITK)
 
 Copyright (c) German Cancer Research Center,
 Division of Medical and Biological Informatics.
 All rights reserved.
 
 This software is distributed WITHOUT ANY WARRANTY; without
 even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.
 
 See LICENSE.txt or http://www.mitk.org for details.
 
 ===================================================================*/
 
 #include "mitkUSTelemedScanConverterPlugin.h"
 #include "mitkImageWriteAccessor.h"
 
 USTelemedScanConverterPlugin::USTelemedScanConverterPlugin( )
   : m_Plugin(NULL), m_OutputImage(NULL)
 {
 }
 
 USTelemedScanConverterPlugin::~USTelemedScanConverterPlugin( )
 {
   ReleasePlugin();
 }
 
 // -- internal Telemed API function
 HRESULT __stdcall USTelemedScanConverterPlugin::QueryInterface(const IID& iid, void** ppv)
 {
   reinterpret_cast<IUnknown*>(*ppv)->AddRef() ;
   return S_OK ;
 }
 
 // -- internal Telemed API function
 ULONG __stdcall USTelemedScanConverterPlugin::AddRef()
 {
   return InterlockedIncrement(&m_cRef) ;
 }
 
 // -- internal Telemed API function
 ULONG __stdcall USTelemedScanConverterPlugin::Release()
 {
   if (InterlockedDecrement(&m_cRef) == 0)
   {
     delete this ;
     return 0 ;
   }
   return m_cRef ;
 }
 
 STDMETHODIMP USTelemedScanConverterPlugin::InterimOutBufferCB (
   PBYTE pBufferInterim,
   int nInterimBufferLen,
   PBYTE pBufferOut,
   int nOutBufferLen,
   int nOutX1,
   int nOutY1,
   int nOutX2,
   int nOutY2
   )
 {
   if ( ! m_OutputImage ) { return S_FALSE; };
 
   // initialize mitk::Image with given image size on the first time
   if ( ! m_OutputImage->IsInitialized() )
   {
     unsigned int dim[]={(nOutX2 - nOutX1), (nOutY2 - nOutY1)}; // image dimensions
 
     m_OutputImage->Initialize(mitk::MakeScalarPixelType<BYTE>(), 2, dim);
   }
 
   // lock the image for writing an copy the given buffer into the image then
   mitk::ImageWriteAccessor imageWriteAccessor(m_OutputImage, m_OutputImage->GetSliceData(0,0,0));
   m_OutputImage->SetSlice(pBufferOut);
 
   return S_OK;
 }
 
 void USTelemedScanConverterPlugin::ReleasePlugin()
 {
   if (m_Plugin != NULL)
   {
     // remove this callback from Telemed API plugin
     m_Plugin->SetCallback(NULL,USPC_BUFFER_INTERIM_OUTPUT);
   }
-  SAFE_RELEASE(m_Plugin);
 }
 
 void USTelemedScanConverterPlugin::SetOutputImage(mitk::Image::Pointer outputImage)
 {
   m_OutputImage = outputImage;
 }
 
 STDMETHODIMP USTelemedScanConverterPlugin::SetScanConverterPlugin(IDispatch* plugin)
 {
   // make sure that there is no scan converter plugin registered already
-  ReleasePlugin();
+  this->ReleasePlugin();
 
   HRESULT hr;
 
+  // it is ok to call this method with a NULL plugin to remove
+  // a previous callback
   if (plugin == NULL)
   {
-    MITK_WARN("IUsgfwScanConverterPluginCB")("ScanConverterPlugin")
-      << "Plugin must not be NULL when calling SetScanConverterPlugin.";
-    return S_FALSE;
+    MITK_INFO("IUsgfwScanConverterPluginCB")("ScanConverterPlugin")
+      << "NULL plugin set to the scan converter. The callback for the previous plugin is removed now.";
+    return S_OK;
   }
 
   // get Telemed API plugin from the COM library
   Usgfw2Lib::IUsgScanConverterPlugin* tmp_plugin;
   hr = plugin->QueryInterface(__uuidof(Usgfw2Lib::IUsgScanConverterPlugin), (void**)&tmp_plugin);
 
   if (FAILED(hr))
   {
     MITK_WARN("IUsgfwScanConverterPluginCB")("ScanConverterPlugin")
       << "Could not query com interface for IUsgScanConverterPlugin (" << hr << ").";
     return hr;
   }
 
   // get the converter for scan lines from the COM library and
   // save it as a member attribute
   hr = tmp_plugin->get_ScanConverter((IUnknown**)&m_Plugin);
 
   if (FAILED(hr))
   {
     MITK_WARN("IUsgfwScanConverterPluginCB")("ScanConverterPlugin")
       << "Could not get ScanConverter from plugin (" << hr << ").";
     return hr;
   }
 
   SAFE_RELEASE(tmp_plugin);
 
   // now the callback can be set -> interface functions of this
   // object will be called from now on when new image data is
   // available
   hr = m_Plugin->SetCallback(this,USPC_BUFFER_INTERIM_OUTPUT);
 
   if (FAILED(hr))
   {
     MITK_WARN("IUsgfwScanConverterPluginCB")("ScanConverterPlugin")
       << "Could not set callback for plugin (" << hr << ").";
     return hr;
   }
 
   return S_OK;
 }
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