Fortran f90 unexpected values ???

Hello,

I have a problem that I cannot explain. When I compile my code with gfortran or ifort I get different errors. The code is reading input data and then in three loops performs summations, etc ... The output I want is an array. When I compile my code with gfortran, the output gives the expected results except for two numbers which gives NaN. In the case where I complile with ifort, the same run with the same input data as before, gives correct values for the data where I had NaN, but now gives unexpected high values (10^200 ???) for some other output data. How can I resolve the problem and how is it explained??

Thanks,

Marios