ProblemThe file download dialog box appears when a file is downloaded in Microsoft Internet Explorer. On this dialog box a check box is available to disable it, it`s called "Always ask before opening this type of file".
Even though the correct user settings have been configured the setting is not remembered.
CauseThe registry keys needed to save this setting contain REG_NONE values. This is an unsupported registry type, which is used by Microsoft in some cases.
The MSDN article http://msdn.microsoft.com/en-us/library/windows/desktop/ms724884(v=vs.85).aspx describes that this is a "NULL" type.
Any attempt to programmatically read such a registry value results in "nothing". Nor is it possible to programmatically write such a value into the registry.
An example of a registry key that holds such a value can be found here:
This key saves the File Download preference for file downloads in Internet Explorer.