Hi Amal,
Sorry for the delay in responding.
I am not able to reproduce the issue that you mentioned here. As per your requirements I have created one sample, merge the cells and autofit the rows. Here it works fine. I have tested this issue in Win Xp with service pack2,.Netframework 3.5, Office 2003.
Please refer the below code snippet:
[C#]
sheet1.Range["A9:A11"].Merge();
sheet1.Range["B9:B14"].Text = "This is the Autofit Rows";
sheet1.Range["B9:B14"].AutofitRows();
Here is the sample for your reference:
http://websamples.syncfusion.com/samples/XlsIO.Windows/42897/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?
Also please provide your system details and the office version.
Regards,
G.Yavana