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>>Do you know where can I find why I don't have SiteID in the DataSet? Is there any other file in addition to the ASPX/ASPX.cs I have to re-check?
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>
> There isn't an easy way to answer this, since it could be failing just about anywhere in your code. I'd set a few breakpoints at various points and view the dataset to see what data and columns are included. The easiest place to start is probably right before you copy the dataset.

I set a breakpoint in the create Excel method. If I just open my page and then immediatelly press Excel button, the column is not there. If I first do some selects, the column is there (since I create it in the code). In the ASPX itself I also have this column defined in the select statement of the DataSource (though I added it later in ASPX itself). Somehow this is not enough for unknown reason...

Anyway, plan to install Visual Studio 2008 in a few minutes (currently using 2005 and don't want to un-install it). Wish me luck...