We need to check the log file to put more light. Use Drop Box http://db.tt/v0soB3XD to upload the log file if the issue doesn't get resolved after following the steps below.
Log File location: c:\program files(x86)\common files\adobe\installer
>> Uninstall Photoshop 5.1 from the Creative Suite Standard 5.5 installer.
>> Uninstall it from Control Panel - Program and features.
>> Restart the computer.
>> Install Photoshop from the Creative Suite Standard 5.5 disk.
>> Run the update.
You could ask in the ACR forum.... I get the ugly suspicion that this may be a compatibility issue since you are using multiple products, each of which has its own version to access ACR...
Moving this discussion to the Adobe Camera RAW forum.
Thank you for the suggestion. Tried it but it did not work when I just uninstalled photoshop but it did solve my problem when I uninstalled and then reinstalled from disk the entire Creative Suite. The original install was a trial download and perhaps that is why I had the problem. Thanks again.