Array_diff function failing in some cases

array_diff function failing if the array has any of the two identical element.
For example if I apply this function for array:
@array1=qw(4,5,4,1,2) and @array2=qw(4,5,4,1,2)

then it will fail...and say the Arrays dint match.

But if I give only the unique elements in the array, it works, Eg.
@array1=qw(4,5,1,2,3) and @array2=qw(4,5,1,2,3).

...I am planning to use this function to apply on big data base.
So can anybody tell me the reason or alternate for this.

Can you post the array_diff function itself please?