I think the problem is in the line
foreach (DataRow row in dstFillState.Tables[0].Rows) // Loop over the rows.
{
strHTML = strHTML + "<option value=" + (string)row["Id"] +">" + (string)row["State"] +"</option>";
}
you should use like this
foreach (DataRow row in dstFillState.Tables[0].Rows) // Loop over the rows.
{
strHTML = strHTML + "<option value='" +row["Id"].ToString() +"'>" + row["State"].ToString() +"</option>";
}
or even
foreach (DataRow row in dstFillState.Tables[0].Rows) // Loop over the rows.
{
strHTML = strHTML + "<option value='" + row["Id"] +"'>" + row["State"] +"</option>";
}
here is a good example
Invalid postback or callback argument. When dropdown list populated with jquery and there is a postback