Thomas,
First, the error 88 occurs because Sizer buttons support a very limited list of properties, including:
BringToTop,Col,Cols,CtlName,Enabled,Height,hWnd,Key,Left,Line,Lines,LookAndFeel,MaxValue,MinValue,ObjectID,OnTipCtl,Parent,Top,Visible,Width,
Second, with WindX you're in turbo mode, so not all errors are reported.
See:
https://manual.pvxplus.com/page/windx/turbo.htm