Penso che a causa del vostro primo tentativo di eseguire direttamente il .dll, la voce “Windows Photo Viewer” punti ancora al .dll invece che al rundll32, che ovviamente non si può eseguire direttamente.
Provare ad aggiungere quanto segue al registro:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll]
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell]
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open]
"MuiVerb"="@photoviewer.dll,-3043"
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\print]
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\print\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\print\DropTarget]
"Clsid"="{60fd46de-f830-4894-a628-6fa81bc0190d}"
Fonte )
Se questo non funziona, provare a cercare nel registro di sistema Windows Photo Viewer e photoviewer.dll per vedere se ci sono riferimenti a photoviewer.dll che vengono chiamati direttamente (senza rundll32).