Your system is clean--that dialog by AVG Free is nothing to be concerned about. Many legit Windows files will be reported as 'changed' when you scan with AVG Free. As long as they are not flagged as 'infected', no worries. For a detail on what exactly that 'changed' status means by AVG, I would suggest you contact their site and ask them to explain it to you.
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Member of ASAP since 2005
Member of UNITE since 2006
"It is one life whether we spend it laughing or weeping." "Take the time to laugh--it is the music of the soul."