Open Terminal from /Applications/Utilities and paste in the below command, then hit enter.
I think this is a bug in the install routine in some apps. Every time a Skitch update comes out I get this also.
Code:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain user;killall Finder