User32 provides the functionality to intercept every MessageBox function and automatically choose the default button. Not all message box windows are produced through the standard MessageBox function; therefore, this feature might not operate on all windows.

To instruct NTUSER to intercept messages, an additional key and values are required in the HKLM\System\CurrentControlSet\Control registry key. You might need to create the registry key and values on your system, as follows.

To set up your system to automatically reply to a message box without displaying it

1. In the HKLM\System\CurrentControlSet\Control registry key, create a new key named Error Message Instrument.
   
2. Under the Error Message Instrument key, add the values of type REG_DWORD from the following table.
   

   Value	Data	Description
   EnableDefaultReply	0x00000001	Enables the Enable Default Reply feature.
   EnableLogging	0x00000001	Enables event logging.

3. Under the Error Message Instrument registry key, add one of the LogSeverity values of type REG_DWORD from the following table.
   

   Value	Data	Description
   LogSeverity	0x00000000 = EMI_SEVERITY_ALL	All message box events are logged.
   LogSeverity	0x00000001 = EMI_SEVERITY_USER	Message box events with the dwStyle parameter defined are logged, including MB_USERICON, MB_ICONASTERISK, MB_ICONQUESTION, MB_ICONEXCLAMATION, and MB_ICONHAND.
   LogSeverity	0x00000002 = EMI_SEVERITY_INFORMATION	Errors, warnings, questions, and information are logged. Message box events with no dwStyle parameter or dwStyle = MB_ICONUSER are not logged.
   LogSeverity	0x00000003 = EMI_SEVERITY_QUESTION	Errors, warnings, and questions are logged. Information, events with no style, and user-defined severity levels are not logged.
   LogSeverity	0x00000004 = EMI_SEVERITY_WARNING	Only errors and warnings are logged.
   LogSeverity	0x00000005 = EMI_SEVERITY_ERROR. (EMI_SEVERITY_MAX_VALUE)	Only errors are logged.

To log message information to the event log

1. In the HKLM\System\CurrentControlSet\Services\EventLog\Application registry key, create a new key named Error Instrument.
   
2. Under the Error Instrument key, add the registry values from the following table.
   

   Value	Type	Value
   TypesSupported	REG_DWORD	0x00000007
   EventMessageFile	REG_EXPAND_SZ	%SystemRoot%\System32\User32.dll

You must reboot your target system for the changes to take effect.

 See Also

Other Resources

Message Box and Balloon Pop-Up Interception