I see, it works only on Vista and later, are you trying with win 7? see requirement section on https://docs.microsoft.com/en-us/windows/win32/api/commctrl/nf-commctrl-monthcal_sizerecttomin. It is a shame,
We have modified methods New() and Initiate() using this code:
aRect = MonthCal_GetMinReqRect( ::hWnd )
SetWindowPos( ::hWnd, 0, ::nLeft, ::nTop, ;
Max( ::nWidth, aRect[ 4 ] ) - ( ::nLeft * 2 ), ;
aRect[ 3 ], nOr( SWP_NOZORDER, SWP_NOMOVE ) )many thanks