See how this goes. Back up the reg fist....just in case.
Open With - Not Working or Listed
Check your settings here:
HKEY_CLASSES_ROOT\Applications. Select the associated sub-key, if 'NoOpenWith' is listed, delete it.
This setting allows you to control whether the checkbox to save the "Open With" program is available when an unknown file type is opened.
HKEY_CLASSES_ROOT\Unknown\shell\openas\command
To enable the checkbox set the (Default) value to "rundll32.exe shell32.dll,OpenAs_RunDLL %1".
Return to the desktop and press F5 for the change to take effect.