zk.wpd JS error, with window inside window

I am gettting JS errors on zk.wpd >TypeError: Cannot read property 'offsetHeight' of null>>Failed to mount: Cannot read property 'offsetHeight' of null>>TypeError: ao is null>>in zk.wpd script file I have narrowed it down to a cause... that is I have a zul page where i have created a child window to be opened as a popup i.e. initially hidden, inside an parent window, but for some reason it works properly for few times and than all of a sudden it starts to throw strange JS errors from zk.wpd as i mentioned in my initial question. If i comment the child window and run application, there is no issue at all. I can't understand as of now, why it is happening but will update this post again if I find a solution. **the child window is** it is a part of **parent window** with few other grids and listboxes `CHILD WINDOW GOES HERE` `ALONG WITH OTHER GRIDS AND OTHER tags` ``