Hello Manoj,
This one is very hard to tell. Are you using some sort of caching? Or maybe the browser uses GET caching (so you need to add time stamp to the URL you are opening with javascript). Where are you binding the grid - are you using InitializeDataSource, etc.
It is really tough to tell without seeing the implmentation details first. By the way, I can recommend using our own WebDialogWindow component instead of window.open - much better results (better interface, better programmatic control over the window, skins, etc) - you can see WebDialogWindow in action here:
It is very hard to say from this description and I am not 100% sure this is related to the grid (could be, just have not seen anything like that recently). I believe in cases like that the best approach would be to contact developer support directly, if possible, with a small subset of your project reproducing the issue.
Developer Support can be reached at:
http://ko.infragistics.com/support/default.aspx