I'm facing the problem of NULL being defined twice. The scenario arises when part of the project is in C code. Consequently, I have to include stdio.h in my file. Obviously, NULL is defined in this file. Now, this NULL is also defined in e32std.h and that too without an #ifndef.
Hence, a build would result in a clashing of definitions of NULL. I think life would have been much easier had e32std.h contained a #ifndef to check if NULL has already been defined.
I had this problem as well. If I remember correctly, it occurs when C standard library header files are included before e32std.h (I think). If you switch the order of your includes, it should work out.