Adobe Reader 9.4.2 - PDFs won't open in IE 8 & IE 9

Question

The recent Adobe Reader 9.4.2 is causing issues with PDFs opening in IE 8 and 9 browsers.  Prior to this update our users have had no issues with opening PDFs generated by our website.
Our website generates USPS labels using Siberix ReportWriter software.  We have not released any updates for at least a month.  Again, before the release of Adobe Reader 9.4.2, there was no issues with our website's PDFs opening in IE browsers.
User System Specs:
Windows XP SP3 and Windows 7 Ultimate
Adobe Reader 9.4.2
Internet Explorer 8 - "File Download" window issue
Internet Explorer 9 - "File Download" window issue
Firefox 3.6.13 - No Issues
Chrome 9.0.597.98 (with Adobe Reader 9.4.2 plugin enabled and Chrome PDF Viewer disabled) - No Issues
The "File Download" window states the following (in addition to a Save and a Cancel button): "The file you are downloading cannot be opened by the default program.  It is either corrupt or it has an incorrect file type.  As a security precaution, it is recommended that you cancel the download. ..."
We have the following workarounds to address this issue with our customers, but they are not ideal:
Update to Adobe Reader X
Disable "Display PDF in browser" Reader option
Don't update Adobe Reader 9 to 9.4.2
Install other PDF Reading software.
Any solutions to this issue would be appriciated.
Thanks

Answer 1

We are experiencing the same problem, as I mentioned below. I did some research and experimentation, and have a ... workaround. It's not completely satisfactory, but we will go with it until we have a complete solution. Perhaps the following will help others and spur some research in the right direction.
First, a quick review. The problem does not occur with PDFs located on disk; it only occurs with direct streaming of PDF data. Let's also note that the problem does NOT occur with other browsers, e.g. FireFox. So ... technically the problem is not an Adobe Reader problem and we're all on the wrong forum.
My specialty is databases and I'm certainly no expert in this area, but from what I'm able to gather the problem is instead with how IE is recognizing and responding to the MIME type of the streamed data. We're all setting the contenttype to "application/pdf" (or similar) or we wouldn't even be here. But I'm concluding that something - some windows update - has changed the way IE on clients or (in my case) IIS on the server is handling that data stream. If any of you experiencing this issue have servers other than IIS, then the problem is on the client side, I'd say.
Aaaaaanyway, the following articles are old, but helped me:
http://forums.asp.net/p/1036628/1436084.aspx
http://www.techper.net/2008/02/27/4-ways-to-stream-pdf-and-some-tips/
To cut to the chase, the workaround we're going with for now is to add the following to the http response header (this is C#/ASP.NET code):
Response.AppendHeader("content-disposition", "attachment;filename=myfile.pdf");
That causes a popup dialog to appear asking the user to open or save the PDF, something that is familiar to most everyone. If the user asks to open the file, it appears in a browser window just as it did before this problem occurred. Again, this is a temporary solution, but at least the user can see the PDF data in a browser with one extra mouse click.
If an Adobe tech support person or anyone with more experience in this area knows the final solution, I'd LOVE to hear it. Please reply here or in email.
Thanks and good luck all.
BillyB