crashes on some systems.. please help

i've run out of ideas.. i'm working with a Tab Control and on some systems the program crashes when accessing a global HWND[2] for the two dialogs i use here. on my system it's all ok.

anyone know whats wrong here?

Code:

HWND phDlg[2];

// ...

// in the dialog procedure i catch WM_INITDIALOG and initialize phDlg.
// hwndDlg is the handle of the dialog the tab is placed on:

phDlg[0] = CreateDialog(hInst, MAKEINTRESOURCE(IDD_TABDIALOG1), hwndDlg, (DLGPROC)TabDlg1Proc);
phDlg[1] = CreateDialog(hInst, MAKEINTRESOURCE(IDD_TABDIALOG2), hwndDlg, (DLGPROC)TabDlg2Proc);

// then i catch TCN_SELCHANGING and TCN_SELCHANGE and show the appropriate dialog:

int nCurSel = TabCtrl_GetCurSel(hwndDlg);
if ((nCurSel >= 0) && (nCurSel <= 1))
	ShowWindow(phDlg[nCurSel], SW_SHOW);

it works fine when i pass hwndDlg (from the parent window) to ShowWindow() which doesnt make sense of course but helped to localize the error. however, phDlg[0] or phDlg[1] as argument causes the app to crash - on some systems.

are you checking to make sure CreateDialog returned valid handles?