Question: When running msbuild.exe with ANT's exec task, errors in the .net code do not result in the build process failing.

Why would this be?

Answer: 
I arrived at a solution and used `Exec`'s `failonerror`, works like a charm.
What do you let the msbuild task do ?

When I used NAnt previously, I used the task to build a VS.NET solution.

Right now, I'm not using NAnt anymore, I use msbuild instead. :)