This code fails because you are passing in a string. The Columns collection does not contain any strings, it contains a UltraGridColumn objects.

You should be using the Exists method to see if a column exists with the specified key.

Resolved with following code; but I still don't know why the previous one failed:

foreach(var  col in grid.DisplayLayout.BandsSerializer[0].Columns)
{
    if( col.Key.Equals("Gas"))
           col.Width = iPresetValue;

}

I've read Mike's post, he suggested not to use BandsSerializer. But my case is to resume stored Grid display information (column width etc)