Hi Jogesh,
You can disable the given Tab in tabbedMDIManager by using TabPageAdv's TabEnabled property. Please refer the following code snippets which illustrates the same:
[ C# ]
this.tabbedMDIManager1.GetTabPageAdvFromForm(MDIChild2).TabEnabled =false;
Also kindly take a look at the attached sample.
http://websamples.syncfusion.com/samples/Tools.Windows/F61013/Main.htmPlease let me know if you have any other queries.
Thank you for using Syncfusion products.
Regards,
Rajesh C