C#

private void CreateStyles(DataGrid dg)
{
  DataGridTableStyle style = new DataGridTableStyle();
  style.MappingName = "IssueHistory";

  DataGridTextBoxColumn DetailID = new DataGridTextBoxColumn();
  DetailID.MappingName = "DetailID";
  DetailID.WidthChanged += new EventHandler(this.SaveIssueGrid);


  RegistryKey softwareKey = Registry.LocalMachine.OpenSubKey("Software");
  RegistryKey SC = softwareKey.OpenSubKey("SC");
  
  if( SC != null)
  {
    RegistryKey Param = SC.OpenSubKey("Param");

    if(Param != null)
    {
      DetailID.Width = (int)Param.GetValue("IHDetailIDWidth",50); // <-- problem line
    }
  }
  // code here to add style to dg
}

void SaveIssueGrid(object sender, EventArgs e)
{
  RegistryKey softwareKey = Registry.LocalMachine.OpenSubKey("Software",true);
  RegistryKey SC = softwareKey.CreateSubKey("SC");
  RegistryKey Param = SC.CreateSubKey("Param");	

  Param.SetValue("IHDetailIDWidth",this.dgIssueHistory.TableStyles["IssueHistory"].GridColumnStyles["DetailID"].Width); // <- problem line
}

<code>
		private void btnRead_Click(object sender, System.EventArgs e)
		{
			RegistryKey softwareKey = Registry.LocalMachine.OpenSubKey(@"Software\SC\Param");
			if ( softwareKey != null )
			{
				int x = (int)softwareKey.GetValue("IHDetailIDWidth", 50); // <-- problem line    
				label1.Text = x.ToString();
			}  
		}

		private void btnWrite_Click(object sender, System.EventArgs e)
		{
			RegistryKey softwareKey = Registry.LocalMachine.OpenSubKey(@"Software\SC\Param", true);  
			softwareKey.SetValue("IHDetailIDWidth",this.Width); // <- problem line
		}
</code>

Csharp™  the coder formally known as dynamic

DetailID.WidthChanged += new EventHandler(MyIDColumnWidthChanged);<br />

strConn += " Data Source=" + Application.StartupPath + "\\foo.mdb;";

strConn += " Data Source=" + Path.Combine(Application.StartupPath, "foo.mdb") + ";";

StringBuilder sb = new StringBuilder();
//Build the rest of your string here using the Append and AppendFormat methods
sb.AppendFormat(" Data Source={0};", Path.Combine(Application.StartupPath, "foo.mdb"));