This is a heads up rather than a question -
My users reported issues with a site that allows previewing of PDF files my company uploads to it (the site is business related and requires an account so I can't post the details). When previewing pdf's IE8 would either hang trying to display the pdf, or display it but then hang if the user tried to browse away from it. Putting the browser in to IE7 browser mode (via F12 when IE is running) fixed the problem and has been the workaround whilst I looked into the problem.
My admin account had no issues with the site, so I ran a procmon session against my admin account and again against a user account that had the issue. Comparing the two I could see that my admin session was spawning acroread32.exe, but the user account wasn't - even when the user account displayed the pdf. there was no obvious reason why.
After chasing around for some time I found the problem was a group policy setting applied to the users which disabled Accelerators within IE8 (google is your friend for info about Accelerators). Once the policy setting was reversed against a test user account the site worked perfectly. As IE7 doesn't run Accelerators it also explained why the workaround was working.
What is bizarre is that the reader doesn't even install an Accelerator? It looks like on this site Reader is using whatever components are used to run Accelerators despite not loading one itself.
As we are a finance house with an understandably paranoid security team allowing Accelerators generally wasn't an option. I did find an additional group policy setting however -
Within User\admin templates\windows components\internet explorer\accelerators
The setting is 'use Policy Accelerators'
This enables Accelerator functionality within IE8 but restricts the allowed Accelerators to a list that is specified within other Group Policy settings in the same area. Enabling the setting but not defining a list of allowed Accelerators got Adobe working without allowing my users any additional access to install / run any Accelerator components. I'm piloting this fix now but things are looking good so far.
Could you please try disabling protected mode in Reader (Launch Reader > choose Edit > Preferences > General > uncheck "Enable Protected Mode at startup), and let me know if the problem goes away?
Protected mode on or off made no difference. In fact every combination of settings were tried within the reader and none made any difference. The group policy fix outlined in my post was rolled out across the company last night and everyone is now accessing pdf's from the site without problems. We are currently running version 10.0.1 but I had the same problem when trying the latest version from the adobe site.