OS and Software > Microsoft Help > Permanently Remove Check Mark In Always Use This Program---

Method A:

1. Open regedit and goto:

HKEY_CLASSES_ROOT\Unknown\shell\opendlg\command

2. In right-side pane, change value of "Default" key to as following:

%SystemRoot%\system32\rundll32.exe %SystemRoot%\system32\shell32.dll,OpenAs_RunDLL %1 %2

NOTE: We have only appended %2 at last of default value. You can use any number from 2-9.