https causing "CryptographicException: Padding is invalid and cannot be removed"

we developed a page for a client that returns some results from an SQL table. there is a link to download the results as a CSV file. on the live server, when connected via HTTPS, it throws an error. file downloads fine over normal HTTP.

the annoying thing is, the file downloads fine over HTTPS on our internal development server. both are running IIS 6, asp v2.0.50727, and sql 2005. the site is being served off one machine, not a server farm. is being declared in web.config, with validation="SHA1". here is the code that is generating the csv file:

protected void DownloadNewReport(object sender, EventArgs e)
{
UpdateDataTable();

DataTable csvdt = new DataTable();
csvdt = dv.ToTable();

foreach (ListItem i in columnsCheckBoxList.Items)
{
if (!i.Selected)
{
csvdt.Columns.Remove(i.Value);
}
}

if (csvdt.Rows.Count > 0)
{
B ...