I ran into a problem with using the dcopy subroutine of MKL. When compiling and running the included small test using gfortran and intel MKL version 11, it works fine on my Xeon machines, but fails on the Opteron machines. Both the integer*4 and integer*8 versions of the 64-bit libraries of MKL seem to have this problem. ACML has the same issue, but only in their integer*4 64-bit library. The test program works fine with the older version 10.1.3.027 of MKL.