Rilly obnoxious thread problem

In my worker thread, if I pass the HWND of my dialog as pParam and in the thread do this:

CSolveDlg *pDlg = (CSolveDlg*) CWnd::FromHandle((HWND)pParam);
CLogicPaintDoc *pDoc = pDlg->m_pLogicPaintDoc;
pDoc->UpdateAllViews(NULL);

I get an error. If I do this, passing a pointer to the dialog as pParam:

CSolveDlg *pDlg = (CSolveDlg*) pParam;
CLogicPaintDoc *pDoc = pDlg->m_pLogicPaintDoc;
pDoc->UpdateAllViews(NULL);

I get a different kind of error. What should I do?