Error C2440: '=' : cannot convert from 'wchar_t *' to 'unsigned char *'

Richard is correct. In general, in C++ you should use new and delete but even better is to use STL objects. A std::vector<puchar> would likely work for you.

In the rare instances I have use calloc and free I use this little macro :

#define AllocateMemory(count,type)	(type*)calloc(count,sizeof(type))

// example usage to get 50 pointers :

PUCHAR * m_buffer = AllocateMemory( 50, PUCHAR );

No casting is necessary because it is done in the macro.

Do you really want 50 pointers or do you want an array of 50 bytes? It is not clear from your question because it mixes them. The example shows how to get 50 pointers. Using the macro, here is how to get 50 bytes :

UCHAR * m_buffer = AllocateMemory( 50, UCHAR );

PUCHAR m_buffer = AllocateMemory( 50, UCHAR );
// or
UCHAR* m_buffer = AllocateMemory( 50, UCHAR );

Your code has (at least) two problems.

1. You are trying to assign a block of dynamic (heap) allocated memory to an array (which is, by the way, already allocated on the stack).
2. You are assigning incompatible types, w_char and unsigned char.

Please note, calloc is not the C++ way for allocating dynamic memory (new it is) and, anyway, new is seldom needed. You might, instead use std::array, e.g.

std::array<unsigned char, 50> ab;
std::array<wchar_t, 30> aw;

for fixed-size memory or, as suggested, std::vector, e.g.

std::vector<unsigned char> vb
std::vector<wchar_t> vw;

for dynamically allocated one.