Internet Explorer 9 Upgrade conflict with Opening PDF Files

I upgraded the default version of Internet Explorer to IE 9 but it brings me an issue while opening PDF files. (An error message is attached as follow). I have tried opening it via Adobe Reader 10 and 9 but nothing works fine. Before upgrading the IE to version 9, I did not encounter any kind of issue related to opening PDF files.
The error message below appeared on the screen:
“The Adobe Acrobat/Reader that is running can not be used to view PDF files in a Web Browser.
Adobe Acrobat/Reader version 8 or 9 is required. Please exit and try again.”

