on beaglebone return string output instead of integer array.

I have a Beaglebone black running debian and I am using python for my requirement. When I run on a wave file, instead of returning numpy array of integers, it returns a string with one or two elements. So, further processing becomes impossible.The error message shows:
IndexError: 0-d arrays can’t be indexed.

But the same program with the above wave file worked fine on ubuntu, which returned integer numpy array output. So, it is not the problem with wave file or the program. Is there anything else I should configure on beaglebone? I installed scipy, numpy and all the packages I use to run the program in ubuntu.