Recently at work, I spent a fair amount of time debugging some strange run-time errors in one of our test tools (after having ported it from Visual Studio 2003 to VS 2005). When starting up a debug build of the tool, I would get the following error message:

An application has made an attempt to load the C runtime library incorrectly. Please contact the application's support team for more information.

This error message turned out to be a red herring, though it pointed me in the direction of the actual culprit: a circular dependency chain of debug and release versions of various Microsoft DLLs. In trying to figure out what was going wrong, I ran across an incredibly helpful article on troubleshooting these kinds of issues. The author presents seven different scenarios that can arise with executables built in Visual Studio 2005, along with solutions for each one. It's a great resource to have if you run into these kinds of problems.