cleaning the registry incorrectly could have removed 'something'--so a re-install of CS6--as mentioned, by others, is probably appropriate----uninstall CS6--find and download the 'Adobe Cleaner Tool' then run that to remove traces of the previous CS6 install--before you re-install.
re: defrag vs clean---
defrag finds all the scattered pieces of files that are written to a hard drive and makes them contiguous so the machine can locate and load the files more efficiently
clean--removes temp files, obsolete registry entries and a host of other things (depending on how CCleaner is configured) also CCleaner allows easy access to startup items and restore points---
in other words defrag is like 'organize' and clean is like 'remove the crud'