Run/Start "regedit"
Then Goto HKEY_CLASSES_ROOT\CLSID\
There will be loads of numbers and letters in brackets example "{0000AB0-0000-00A0-A000-0A0B0000D00}"
Look for one called "{4380C993-0C43-4E02-9A7A-0D40B6EA7590}"
Then Click Delete (DEL) and it will remove Defraggler from Context Menu
i had same problem when disabling and this sorted it.
I hope its helps