realft() problem

[fortran]

I am using realft() in fortran. It works perfectly for arrays of size 4096 and 16384, but when I increased to 65536 or larger the fourier transform gives infinity. I checked with 2 different compilers, Intel fortran (windows) and PGF (unix). All th numebrs I tried are power of 2. Do you have any ideea why is happenig and if I can solve it some how?

Best,

Cristian