Now it appears again, even without any debug breakpoints occuring before.
This is the call stack when the assertion fails:
  mfc71ud.dll!CWnd::GetWindow(unsigned int nCmd=5)  Line 276 + 0x2b C++
> XTP9700Libud.dll!CXTPPopupBar::Animate()  Line 772 + 0x16 C++
   XTP9700Libud.dll!CXTPPopupBar::Popup(CXTPControl Popup * pControlPopup=0x04ad0548, int bSelectFirst=0)  Line 836 C++
   XTP9700Libud.dll!CXTPControlPopup::OnSetPopup(in t bPopup=1)  Line 181 + 0x3d C++
  XTP9700Libud.dll!CXTPCommandBar::SetPopuped(int nPopuped=1, int bKeyboard=0)  Line 469 + 0x12 C++
   XTP9700Libud.dll!CXTPControlPopup::OnSetSelected (int bSelected=1)  Line 141 C++
  XTP9700Libud.dll!CXTPCommandBar::SetSelected(int nSelected=1, int bKeyboard=0)  Line 419 + 0x33 C++
   XTP9700Libud.dll!CXTPCommandBar::OnMouseMove(uns igned int __formal=0, CPoint point={...})  Line 301 + 0x1b C++
  mfc71ud.dll!CWnd::OnWndMsg(unsigned int message=512, unsigned int wParam=0, long lParam=852012, long * pResult=0x0012dabc)  Line 2164 C++
   XTP9700Libud.dll!CXTPCommandBar::OnWndMsg(unsign ed int message=512, unsigned int wParam=0, long lParam=852012, long * pResult=0x0012dabc)  Line 1865 C++
  mfc71ud.dll!CWnd::WindowProc(unsigned int message=512, unsigned int wParam=0, long lParam=852012)  Line 1745 + 0x1e C++
  mfc71ud.dll!AfxCallWndProc(CWnd * pWnd=0x0012e210, HWND__ * hWnd=0x000f08e0, unsigned int nMsg=512, unsigned int wParam=0, long lParam=852012)  Line 241 + 0x1a C++
  mfc71ud.dll!AfxWndProc(HWND__ * hWnd=0x000f08e0, unsigned int nMsg=512, unsigned int wParam=0, long lParam=852012)  Line 389 C++
  mfc71ud.dll!AfxWndProcBase(HWND__ * hWnd=0x000f08e0, unsigned int nMsg=512, unsigned int wParam=0, long lParam=852012)  Line 209 + 0x15 C++
  user32.dll!_InternalCallWinProc@20()  + 0x28 
  user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 
  user32.dll!_DispatchMessageWorker@8()  + 0xdc 
  user32.dll!_DispatchMessageW@4()  + 0xf 
  user32.dll!_IsDialogMessageW@8()  + 0xdb 
  mfc71ud.dll!CWnd::IsDialogMessageW(tagMSG * lpMsg=0x001540f0)  Line 200 C++
  mfc71ud.dll!CWnd::PreTranslateInput(tagMSG * lpMsg=0x001540f0)  Line 4512 C++
  mfc71ud.dll!CDialog::PreTranslateMessage(tagMSG * pMsg=0x001540f0)  Line 83 C++
   zlzwfud.dll!Zeta::Windows::Forms::EnhancedDialog ::PreTranslateMessage(tagMSG * pMsg=0x001540f0)  Line 194 C++
   ZpCommonDialogud.dll!CXTPDialogBase<Zeta::Win dows::Forms::Specialized::DialogBase>::PreTranslateMessag e(tagMSG * pMsg=0x001540f0)  Line 141 + 0xf C++
   ZpCommonDialogud.dll!Common::Gui::Dialog::RichGu iDialogBase::PreTranslateMessage(tagMSG  * pMsg=0x001540f0)  Line 386 + 0xc C++
  mfc71ud.dll!CWnd::WalkPreTranslateTree(HWND__ * hWndStop=0x001b075e, tagMSG * pMsg=0x001540f0)  Line 3129 + 0x12 C++
   mfc71ud.dll!AfxInternalPreTranslateMessage(tagMS G * pMsg=0x001540f0)  Line 238 + 0x12 C++
   mfc71ud.dll!CWinThread::PreTranslateMessage(tagM SG * pMsg=0x001540f0)  Line 795 + 0x9 C++
  mfc71ud.dll!AfxPreTranslateMessage(tagMSG * pMsg=0x001540f0)  Line 257 + 0xf C++
  mfc71ud.dll!AfxInternalPumpMessage()  Line 183 + 0x18 C++
  mfc71ud.dll!CWinThread::PumpMessage()  Line 916 C++
  mfc71ud.dll!AfxPumpMessage()  Line 195 + 0xb C++
  mfc71ud.dll!CWnd::RunModalLoop(unsigned long dwFlags=4)  Line 4566 + 0x5 C++
  mfc71ud.dll!CDialog::DoModal()  Line 527 + 0xc C++
   zlzwfud.dll!Zeta::Windows::Forms::EnhancedDialog ::DoModal()  Line 97 + 0x8 C++
   zlzwfud.dll!Zeta::Windows::Forms::Specialized::D ialogBase::ShowModal()  Line 69 + 0x8 C++
   ProducerUD.exe!Framework::ProducerMainWindow::On AssetmanagementImages()  Line 2334 + 0x15 C++
  mfc71ud.dll!_AfxDispatchCmdMsg(CCmdTarget * pTarget=0x04a8b918, unsigned int nID=32772, int nCode=0, void (void)* pfn=0x00406348, void * pExtra=0x00000000, unsigned int nSig=53, AFX_CMDHANDLERINFO * pHandlerInfo=0x00000000)  Line 89 C++
  mfc71ud.dll!CCmdTarget::OnCmdMsg(unsigned int nID=32772, int nCode=0, void * pExtra=0x00000000, AFX_CMDHANDLERINFO * pHandlerInfo=0x00000000)  Line 396 + 0x27 C++
  mfc71ud.dll!CFrameWnd::OnCmdMsg(unsigned int nID=32772, int nCode=0, void * pExtra=0x00000000, AFX_CMDHANDLERINFO * pHandlerInfo=0x00000000)  Line 897 + 0x18 C++
  mfc71ud.dll!CWnd::OnCommand(unsigned int wParam=32772, long lParam=0)  Line 2550 C++
  mfc71ud.dll!CFrameWnd::OnCommand(unsigned int wParam=32772, long lParam=0)  Line 320 C++
  mfc71ud.dll!CWnd::OnWndMsg(unsigned int message=273, unsigned int wParam=32772, long lParam=0, long * pResult=0x0012e9b8)  Line 1759 + 0x1c C++
   ProducerUD.exe!CXTPFrameWndBase<CFrameWnd> ::OnWndMsg(unsigned int message=273, unsigned int wParam=32772, long lParam=0, long * pResult=0x0012e9b8)  Line 201 C++
  mfc71ud.dll!CWnd::WindowProc(unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 1745 + 0x1e C++
   ProducerUD.exe!Framework::ProducerMainWindow::Wi ndowProc(unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 471 + 0x14 C++
  mfc71ud.dll!AfxCallWndProc(CWnd * pWnd=0x04a8b918, HWND__ * hWnd=0x001b075e, unsigned int nMsg=273, unsigned int wParam=32772, long lParam=0)  Line 241 + 0x1a C++
  mfc71ud.dll!AfxWndProc(HWND__ * hWnd=0x001b075e, unsigned int nMsg=273, unsigned int wParam=32772, long lParam=0)  Line 389 C++
  mfc71ud.dll!AfxWndProcBase(HWND__ * hWnd=0x001b075e, unsigned int nMsg=273, unsigned int wParam=32772, long lParam=0)  Line 209 + 0x15 C++
  user32.dll!_InternalCallWinProc@20()  + 0x28 
  user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 
  user32.dll!_CallWindowProcAorW@24()  + 0x51 
  user32.dll!_CallWindowProcW@20()  + 0x1b 
   XTP9700Libud.dll!CXTPHookManager::HookWndProc(HW ND__ * hWnd=0x001b075e, unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 158 + 0x1c C++
  user32.dll!_InternalCallWinProc@20()  + 0x28 
  user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 
  user32.dll!_CallWindowProcAorW@24()  + 0x51 
  user32.dll!_CallWindowProcW@20()  + 0x1b 
   ZpCommonCoreud.dll!Common::Gui::SubclassWindow:: WindowProc(unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 152 + 0x5c C++
   ZpCommonCoreud.dll!Common::Gui::HookWndProc(HWND __ * hwnd=0x001b075e, unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 230 + 0x19 C++
  user32.dll!_InternalCallWinProc@20()  + 0x28 
  user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 
  user32.dll!_DispatchClientMessage@20()  + 0x4d 
  user32.dll!___fnDWORD@4()  + 0x24 
  ntdll.dll!_KiUserCallbackDispatcher@12()  + 0x13 
  user32.dll!_NtUserMessageCall@28()  + 0xc 
  user32.dll!_SendMessageW@16()  + 0x49 
  mfc71ud.dll!CWnd::SendMessageW(unsigned int message=273, unsigned int wParam=32772, long lParam=0)  Line 44 + 0x42 C++
  XTP9700Libud.dll!CXTPControl::OnExecute()  Line 315 C++
   XTP9700Libud.dll!CXTPControl::ClickToolBarButton (CRect rcActiveRect={...})  Line 262 + 0x10 C++
  XTP9700Libud.dll!CXTPControlButton::OnClick(int bKeyboard=0, CPoint pt={...})  Line 73 C++
   XTP9700Libud.dll!CXTPCommandBar::OnLButtonDown(u nsigned int nFlags=1, CPoint point={...})  Line 349 + 0x1a C++
   XTP9700Libud.dll!CXTPToolBar::OnLButtonDown(unsi gned int nFlags=1, CPoint point={...})  Line 864 C++
  mfc71ud.dll!CWnd::OnWndMsg(unsigned int message=513, unsigned int wParam=1, long lParam=786782, long * pResult=0x0012fc48)  Line 2164 C++
   XTP9700Libud.dll!CXTPCommandBar::OnWndMsg(unsign ed int message=513, unsigned int wParam=1, long lParam=786782, long * pResult=0x0012fc48)  Line 1865 C++
  mfc71ud.dll!CWnd::WindowProc(unsigned int message=513, unsigned int wParam=1, long lParam=786782)  Line 1745 + 0x1e C++
  mfc71ud.dll!AfxCallWndProc(CWnd * pWnd=0x04aadfa0, HWND__ * hWnd=0x000e0918, unsigned int nMsg=513, unsigned int wParam=1, long lParam=786782)  Line 241 + 0x1a C++
  mfc71ud.dll!AfxWndProc(HWND__ * hWnd=0x000e0918, unsigned int nMsg=513, unsigned int wParam=1, long lParam=786782)  Line 389 C++
  mfc71ud.dll!AfxWndProcBase(HWND__ * hWnd=0x000e0918, unsigned int nMsg=513, unsigned int wParam=1, long lParam=786782)  Line 209 + 0x15 C++
  user32.dll!_InternalCallWinProc@20()  + 0x28 
  user32.dll!_UserCallWinProcCheckWow@32()  + 0xb7 
  user32.dll!_DispatchMessageWorker@8()  + 0xdc 
  user32.dll!_DispatchMessageW@4()  + 0xf 
  mfc71ud.dll!AfxInternalPumpMessage()  Line 188 C++
  mfc71ud.dll!CWinThread::PumpMessage()  Line 916 C++
  mfc71ud.dll!CWinThread::Run()  Line 637 + 0xb C++
  mfc71ud.dll!CWinApp::Run()  Line 701 C++
  zlzud.dll!Zeta::Application::Run()  Line 788 C++
  mfc71ud.dll!AfxWinMain(HINSTANCE__ * hInstance=0x00400000, HINSTANCE__ * hPrevInstance=0x00000000, wchar_t * lpCmdLine=0x00020e94, int nCmdShow=1)  Line 49 + 0xb C++
  ProducerUD.exe!wWinMain(HINSTANCE__ * hInstance=0x00400000, HINSTANCE__ * hPrevInstance=0x00000000, wchar_t * lpCmdLine=0x00020e94, int nCmdShow=1)  Line 25 C++
  ProducerUD.exe!wWinMainCRTStartup()  Line 390 + 0x39 C
  kernel32.dll!_BaseProcessStart@4()  + 0x23 
Maybe someone at Codejock can check whether this is an issue with the new library.
Thanks
Uwe