I also encounter this problem.
In my project I link the libraw (I use Visual Studio). Everything works fine.
However if I want to free (using ::free(ptr)) the pointer returned by dcraw_make_mem_image(...) I get an exception
_CrtIsValiHeapPointer(pUserData) documented in dbgheap.c with
/*
* If this ASSERT fails, a bad pointer has been passed in. It may be
* totally bogus, or it may have been allocated from another heap.
* The pointer MUST come from the 'local' heap.
*/
_ASSERTE(_CrtIsValidHeapPointer(pUserData));

I think the problem is caused that the lib is creating the memory, so only the lib itself is allowed to free it afterwards. The application does only seem to have rights to read the memory.
If I also make the free function public in class LibRaw it seems to work, but there should be a more elegant solution ;)

Regards Tobias