Displaying msgbox to close the opened child form.

The problem is that when the user closes the ChildForm this won't automatically set curfrm to null.

One way you could do that would be to handle the child form's FormClosed event and set it to null from the handler. The code would be something like this:

Form curfrm;

String a = " Please Close the other open windows";

private void admissionForm1ToolStripMenuItem_Click(object sender, EventArgs e)

{

   if (curfrm != null)

   {

       MessageBox.Show(a);

       return;

   }

   else

   {

       curfrm = new adfrm1(null); 

       curfrm.MdiParent = this;

       curfrm.FormClosed += curfrm_FormClosed; // add handler

       curfrm.Show();

   }

}

// type this in manually, not via the designer

private void curfrm_FormClosed(object sender, FormClosedEventArgs e)

{

   curfrm = null;

   curfrm.FormClosed -= curfrm_FormClosed; // remove handler

}