These are the things you need to fix broken thumbnail previews in Windows Explorer:

KEYS...
HKEY_CLASSES_ROOT\<file type>\ShellEx
HKEY_CLASSES_ROOT\<file type>\ShellEx\{BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}

String value called (Default) set to...
{7376D660-C583-11d0-A3A5-00C04FD706EC}