Thanks for your answer Johnny. 

In my case removing the TAG sorted out the problem, but I will keep an eye on that issue and if it happens again I will try your method. 

Sorry, I forgot to post our workaround for this (I thought I did already).  If I remember correctly, we were seeing the same thing happen in IE8 and in "IE7 mode".

Here are the 2 options we came up with to work around this problem.  We ended up using option #2.

1. During the InitializeLayoutHandler, "fix" the columns in JavaScript.

function InitWidth(gridName) {
    // Retrieve the grid based on its ID.
    var oGrid = igtbl_getGridById(gridName);

    // Get the Bands collection
    var oBands = oGrid.Bands;

    // Get the columns collection for Band 0
    var oBand = oBands[0];
    var oColumns = oBand.Columns;

    // The column count is equal to the length of the Columns array.
    var count = oColumns.length;
    
    // Create Column Array.
    var colArray = new Array();
    
    // Set each Column Header width.
    for (var i = 0; i < count; i++) {
        colArray[i] = document.getElementById(oColumns[i].Id).firstChild.offsetWidth;
    }

    var oRows = oGrid.Rows;
    var index = oColumns.Index;

    // Loop thru each row in the grid to set the column to the largest cell width.
    for (var i = 0; i < oRows.length; i++) {
        for (var n = 0; n < count; n++) {
            var cell = oRows.getRow(i).getCell(n);
            if (colArray[n] < cell.Element.firstChild.offsetWidth) {
                colArray[n] = cell.Element.firstChild.offsetWidth;
            }
        }
    }

    // Loop thru each Column in the grid to set the Column width to the largest width.
    for (var i = 0; i < count; i++) {
        oColumns[i].setWidth(colArray[i] + 5);
    }
}

2. Set EnableCrawlerDetection="False"
     Do not set columns as Hidden from the code behind, do it in the mark-up
     Make sure the column width values have "px" in them.  (Ex:  Width="200px" instead of Width="200")

Hope that helps you out.

Are you using IE ?, what version?, if so have you tried to run the site in compatibilty view?

Hi, thanks for the response.

No, I don't use the tag and I can't solve the problem.