Different results from Debug and Release builds of the same code

Hello,

I have a time-marching solution to a non-linear PDE using Newton-Raphson iteration method, and once in a while the debug version will not converge while the release version will, or the release version will not converge while the debug version will.  This makes debugging almost impossible. After a lengthy internet search, I thought that the settings for the /fp flag is the culprit. Based on a white paper I ran into on Intel's web site, I set /fp: precise and /fp:source for both the debug and release versions to achieve consistency between different builds. But I still have the same issue. Are there any other settings that I need to modify?

I am using the latest version of the Intel Fortran compiler with Visual Studio 2010, and my target platform is 64bit OS.

Thanks for any help in advance.

Jon