Smart Fix will only work on media files that have been analyzed in the Elements Organizer.
If you do not have the Auto Analyzer turned on in the Organizer, locate the file in the Organizer's Media Browser, right-click on it and select the Analyzer option.
Once the file has been analyzed, return to Premiere Elements and re-add the file to your timeline.
Much more on this feature and how to use it is discussed in my books, if you're interested.
In fact I have already analyzed the file in the Elements Organizer, but still the SmartFix command is not accessible.
I installed Premiere Element 10 on my other computer, a macbook air running Lion where i did not cross the option ’do not show again’ and there I get the SmartFix command accessible.
Therefore it seems that by crossing the ’Do not show again’ option for SmartFix, I lost it totally, even after performing ’Auto analyzer’.
Have you gone to the program's Preferences/General page and check the option to Show All Do Not Show Message?
Yes, the 'Show all do not show again Messages' is checked. In fact all the preferences for my macbook air (where SmartFix works) and my iMac (where SmartFix does not work) are exactly the same.