"bec" is the last 3-hex-digit portion of the object address.
The error message indicates a pointer to a block of freed memory doesn't actually point to free memory. (Either the pointer itself has been changed in some way, or the memory it points to has been overwritten in a way that clobbers a consistency check.)
The most likely cause is that the memory is a freed object instance, but your code as an unretained reference to it and has tried to use it like a "live" instance. Or it may just be a block of non-object memory that has been modified after being freed.
That is to say, this is likely a memory management bug in your code.
You can try setting a symbolic breakpoint at "malloc_error_break", but my guess is that this will be long after the real problem, and won't tell you what really went wrong.