Having Acrobat and Reader on the same Windows system is known to be troublesome and unsupported. You will need to remove Acrobat and re-install Reader or remove both and upgrade to Acrobat 9.3.4.
This is happening cause while installing Adobe Reader 9, you chose to Adobe Acrobat as the default application to associate with PDF files. Hence, the browser is trying to open the PDF with Adobe Acrobat 6 an hence the error.
You can try and uninstall Adobe Reader 9 and installing the same again. But this time, while installing Adobe Reader 9, chose Adobe Reader 9 as the default application for viewing PDF files. And you should be good to go.
Hope you are able to view PDFs in the browser now.!!
Fixed problem by taking to a computer store to find that my hard drive storage was maxed out. I had the hard drive repaced with a larger amount of storage. Problem resulted from inadequate amount of storage space which prevented me from downloading and installing Adobe Reader 9.
Thanks to al that responded.