http://blogs.msdn.com/piyush/archive/2007/04/29/debugging-windows-installer-msi-using-visual-studio-2005.aspxI was struggling to debug my custom action class... Oh gush real pain How to debug this stuff.. i searched and got the simple way to debug Windows Installer (MSI) is to put below cool line in begining of your custom action class code " Debugger .Break"enCommunityServer 2.1 SP1 (Build: 61025.2)http://blogs.msdn.com/piyush/archive/2007/04/29/debugging-windows-installer-msi-using-visual-studio-2005.aspx#4582536Mon, 27 Aug 2007 06:04:58 GMT91d46819-8472-40ad-a661-2c78acb4018c:4582536Alegni<p>I know that you can set an environment variable on the cmd line equal to name of a custom action inside your msi package. &nbsp;Once the Msi starts running and it reaches that custom action, it breaks into your registered debugger. &nbsp;I have been looking for the name of this environment variable, but I can't find it anywhere in the MSDN library.. </p>http://blogs.msdn.com/piyush/archive/2007/04/29/debugging-windows-installer-msi-using-visual-studio-2005.aspx#4582628Mon, 27 Aug 2007 06:14:13 GMT91d46819-8472-40ad-a661-2c78acb4018c:4582628Alegni<p>I found it!</p> <p>set MsiBreak=&lt;name of your custom action&gt;</p>