Cathal,

Just thought I'd mention the procedure I follow doesn't say to build the code in release mode, though that makes perfect sense.  I'm the same guy with the IIS issues, got that solved obviously since I'm up to THIS post. :)  The issue there is, and I'll put this as a separate reply, is that building the site with localhost was causing the default "default" site -- the one live one we don't have assigned to an IP yet, to confuse itself with the new site.  The errors were coming from ITS web.config.  Again, more when I reply to the other post.

I'm following the full source install procedure at http://www.dnnsoftware.com/wiki/page/how-to-install-the-source-package-of-dotnetnuke and it says:

1. Now you can open the solution file you just modified in Visual Studio. It is a large and complex multiple-project solution so be patient and allow all of the projects to be loaded. Since project files may import several custom MS Build target files you may receive one or more warnings regarding the security risk of modified build files. If you downloaded your DotNetNuke source package from the CodePlex downloads page, you can safely ignore those warnings. If you have selected an ASP.Net v 4.0 App Pool in IIS, you may see a dialog box indicating that the website is configured for a different (v 4.0) of ASP.Net than the solution and project files (v 2.0/3.5). DO NOT select “Yes” to change the target version of the solution to v 4.0 unless you understand that you will be creating a non-standard build of the DotNetNuke library and other projects and fully understand the consequences of such a change.
2. The DotNetNuke source packages do NOT include compiled assemblies of all of the various projects in the Website\bin folder (and in v 5.06.00 and later do not even include a Website\bin folder). Therefore you must build the solution and its multiple-projects before starting the actual installation procedure. If you take a look in the solution’s Build Configuration Manager you will note that the website itself (http://localhost/ . . .) is not included in the build. This is correct as it is not currently possible to pre-compile the website itself – only the library code and the various support projects. The website code will be just-in-time compiled when it is loaded upon the first visit and on subsequent visits if it the ASP.Net worker process has been unloaded or recycled.
3. Finally, click on Build … Build Solution. All projects in the solution should now build without error – but perhaps with a few warnings regarding methods marked obsolete, etc. which can be ignored.
4. Close Visual Studio and save the solution/project files if so prompted.

I am back to this because I installed the 7.3 from the source code and got the divide by zero error. I remembered that I had to copy the install zip first.

Anyway, the link mentioned is outdated and doesn't include the stuff Cathal pointed out. It doesn't mention you have to compile in release mode. In fact you don't have to. My 7.2.2 installation is based on the source package and all the projects are in debug mode. Why do you have to build in release mode? Debug or release mode create the same assemblies. Optimizations doesn't affect how DNN works. The wiki page is  also outdated because it doesn't mention dnndev.me.  DotNetNuke_Community_2008 & DotNetNuke_Community.sln don't exist anymore.

There's no mention anywhere on this site what is actually the source of the divide by zero error. Just what the workaround is.

Last, whether the installation had errors or was successful, the installation page always says 'No Installation Log'. Not helpful!