чччДDimitry SibiryakovПервая же ссылка в гугле:
https://stackoverflow.com/questions/6364879/how-to-open-a-default-dialog-for-window-if-shellexecute-fails-due-to-no-file-ass

Имхо, самый классный ответ дал Alex (Gunsmoker):

GunsmokerSimply do not use explicit verb. Using a specific verb like 'open' is a big mistake:

'open' may be not a default verb (for example, it may be 'play', 'edit' or 'run')
'open' may not exists
It is a way more correct to simply pass NULL as verb. The system will automatically select most appropriate verb:

Default verb will be used, if it is set
'open' verb will be used, if no default verb is set
first verb will be used, if no default and 'open' verbs are available
if no verbs are assigned - the system will bring "Open with" dialog
In other words, simple


will show "Open with" dialog.

Only use a specific verb if you want a specific action. E.g. 'print', 'explore', 'runas'. Otherwise - just pass nil.

В копилку, спасибо.