Are you able to open PDF files that are on your local system without any difficulty? If so, that narrows it down to a browser plugin issue. I have seen similar plugin issues that could only be resolved by creating a new Windows profile (Adobe's suggestion which works but is a sledge hammer compared to what the true fix could be) which leads me to believe that the root of the problem lies in the Windows registry. If you are up for testing this theory, simply create a "test" profile on the system (control panel - User Accounts) in question and see if the problem persists in the newly created profile or not.
Let me know the results.
unfortuantely I don't have the permissions to create Useraccounts on my PC.
But I just found a fix at least for Firefox. After the Acrobat Installation the
Firefox Application Preferences Point to "Acrobat Reader 9.1 verwenden (Standard)".
I changed these to "Adobe Acrobat (in Firefox) verwenden". This stopped the window
explosion at least in Firefox. I attach screenshots of the preferences window.
By now I haven't done further investigations on a IE only system.
If you or anybody has the chance to check this, please let me know.
Hello again, Andreas:
I believe I have found the resolution to your browser plugin issue but I'm sure it will require administrative privledges and will require modifying the Windows registry (not something for the faint of heart). If you are interested, check out the knowledgebase article here: http://kb2.adobe.com/cps/328/328233.html
Something you may be able to try that doesn't require admin privledges:
1. Open Reader
2. Click Edit > Preferences
3. Click Internet on the left menu
4. Uncheck "Allow fast web view"
Crosses fingers for you!