In will compile if you write
table.SetWidths(new int[] { tblwidth, });
But it's likely that you don't understand what you are doing yourself. The array should represent not one width, but a set of width of the columns. Do you think you need a table with just one column? Why?
Please see:
http://itextpdf.com/examples/iia.php?id=76[
^].
—SA