There appears to be some confusion on some of the replies so let me make this a little clearer:

Two ASPX pages in the same application:
http://www.myroot.com/PDFPage1.aspx
http://www.myroot.com/PDFPage2.aspx

PDFPage1.aspx has existed for years and works beautifully.

PDFPage2.aspx is a new copy of PDFPage1.aspx.  It does not work as expected

The code that calls the PDF file and displays it is identical in the example code I provided.  There is a difference in that this code is inside different conditional logic blocks on the two pages.  That should not matter, but maybe someone has a different opinion on that topic.

I tested this code multiple times with only one PDF document, so I can verify the code on both pages is being executed.  Both pages are attempting to load the exact same PDF document.  Page1 succeeds and Page2 fails.  The PDF I am using is 60K.

Page1 has worked for PDF documents that range in size from a few K to over 50 MB in size.

Whew.  I hope that makes it perfectly clear.  I hope someone can help me here.  My gut feeling is that the existence of conditional logic is confusing ASP.NET somehow.