MDI child is not getting when anothe child is closed

I have a main form(F1) from this form i open many other forms(mdi forms). First i open a MDI Child form (MDI1). this form has a spread control ans a cell is highlighted. I open another mdi child(MDI2) from from the main Form(F1) (by clicking on the toolbar button on the main form F1). i do some operations in the second Child form(MDI2) and close it. When i close the second child form the form_acvtivated event of MDI1 is fired but the focus is not set to the MDI1.

I am arranging the forms by tile functionality.

How to set focus to the MDI1?

Veeresh Angadi