Sporadic inability to download pdf after upgrade to Asp.Net 4.0 of SSL website

Yesterday we upgraded our SSL website from asp.net 2.0 to asp.net 4.0. Today some clients using IE8 are saying they are having sporadic problems downloading pdf files. They get an error saying something about downloading the aspx page (not the pdf file).  They did note that if they access the site using http instead of https, they do not have an issue.  
To do the upgrade, we did testing of "our_site" using a folder called "our_site4.0".  When we made the switch, we renamed "our_site" to "our_site2.0" and "our_site4.0" to "our_site".  So there is a new folder involved, but all of the folder security setting and user access settings are identical.

Here is the aspx code that outputs the pdf, and it has not changed between 2.0 and 4.0.

 Response.ContentType = "application/pdf"
        Response.AddHeader("content-disposition", "inline; filename=FormPacket.PDF")
        Response.AddHeader("content-length", theData.Length.ToString())
        Response.BinaryWrite(theData)
        Response.End()
        Response.Clear()
        Response.Close()

 I read some articles that talk about issues with no-cache, but we are not using that setting in the code.  Does anyone have any ideas what the issue is? Thank you.