Many thanks for your response, Aviad. Your suggestion turns out to be half the solution. In addition to decorating the base class as you suggest, you must follow that with decorating any derived classes with: [ToolboxItemAttribute(typeof(ActivityToolboxItem))] If you don't do this, the derived classes inherit the [ToolboxItem(false)] from the base class. (I can't take credit for this; the whole solution was suggested to me in another forum.)

AJarrett wrote: P.S. Alfonso might just as well have been referring to Mr. Gates I absolutely agree :) If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.

Thats right that the problem is almost definately not where you think it is. I mean look at the definiton of new. void* __cdecl operator new(size_t nSize) { void* pResult; #ifdef _AFXDLL _PNH pfnNewHandler = _pfnUninitialized; #endif for (;;) { #if !defined(_AFX_NO_DEBUG_CRT) && defined(_DEBUG) pResult = _malloc_dbg(nSize, _NORMAL_BLOCK, NULL, 0); #else pResult = malloc(nSize); #endif if (pResult != NULL) return pResult; #ifdef _AFXDLL if (pfnNewHandler == _pfnUninitialized) { AFX_MODULE_THREAD_STATE* pState = AfxGetModuleThreadState(); pfnNewHandler = pState->m_pfnNewHandler; } if (pfnNewHandler == NULL || (*pfnNewHandler)(nSize) == 0) break; #else if (_afxNewHandler == NULL || (*_afxNewHandler)(nSize) == 0) break; #endif } return pResult; } Look at the for(;;) It should not fail. You have corrupted the heap. Get MMGR from http://www.fluidstudios.com/publications.html . It is an excellent class. Ensure that you carefully read the instructions [ especially the order of includes]. Use it on Debug and Release builds. Check that you have not used new and free or similar. Check for resource leaks. Regards, axe

Silly me, searching on just WM_CTLCOLOR. :-O I see COLORSTATIC is restricted to a thread, but I can work around that. Many thanks, John. Between you and kuphryn I feel the Force may be with me again.