VB6 Application Compatibility With Vista

I have an application that was written in VB6. This application installs properly (w/o error) on Vista machines. Several months ago I posted a question regarding the "Exe. Has Stppped Working" error that came up when this application was run on Vista and subsequently a compatibility file (.sdb) was created that ran with the installer to set compatibility for "Run As Administartor" and "Windows 2000" compatibility. I do not know why these had to be set as they were but after experimenting with the File>>Properties>>Compatibility this was discovered to make this application run successfully under Vista. (Hence the sdb file was created to set these properties globally during installation. The problem is now the same "Exe. Has Stopped" error is coming up again. Without any indication of why or what other items need to be set in the .sdb file I have no way of knowing what else to do to resolve this. We have essentially eliminated all Vista users from potential sales and this is very damaging to our business. The program is being converted to VB.net but it is 400000 lines of code so this process is taking a long time. We need to get it compatible now. Is there a utility that can be run against an application taht will spell out whrer exactly the incompatibility lies so it can be added to the .sdb? Is there a recommended Installer that would work better? Currently using Installshield 2008 Express. Help!!!