Are you using Visual C++ 6.0, Visual C++ 2002, or Visual C++ 2003?
In each case, Measurement Studio installs a Visual Studio add-in that monitors the .uir file for changes and updates the callbacks file as appropriate. Make sure that the add-in is enabled in the Visual Studio environment that you are using. In VC6, the add-in is named LabWindows/CVI VC AddIn. Go to Tools>>Customize>>Add-ins and Macro Files to enable it. In VC2002 and VC2003, this functionality is part of the main Measurement Studio add-in. Go to Tools>>Add-in Manager to enable it.
If the add-in is enabled, and updates still aren't happening, please post a .zip file with your CVI project and your VC project so that we can check it out.