First of all, i find runtime exception when publishing a website pretty odd. This error pops up semi-randomly in two different ASP.NET solutions that I have in Visual Studio 2008.
Odd things like deleting a sub folder (just the contents aren't enough) resolve the issue temporarily til I need to publish again. These solutions "Build Solution" with no errors or warnings, but die when I try to publish.
Specifically, this happens after the "Pre-compiling Web Site" stage.