Hi Ramana,
I am not able to reproduce the issue that you mentioned here. I have created a simple Gridgrouping sample with two datatable. During the page load the first table is binded. Then in button click I have binded the next tabel. Here it works.
Please refer the sample in the below link which illustrates the above:
http://websamples.syncfusion.com//samples/Grid.Windows/F-73433/main.htmPlease have a look at the above sample and if still the issue exists, could you please try reproducing it in the above sample and send us the modified sample so that we could sort out the cause of the issue and provide you a solution?
Regards,
G.Yavana