There are a number of registry locations where entries would show up for all files. Use regedit and search for the culprets looking first at:

HKEY_CLASSES_ROOT\*\shell
HKEY_CLASSES_ROOT\*\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\AllFilesystemObjects\shellex\ContextMenuHandlers

Back up keys before making edits or deletions.