The memory deallocation in ntop collides with the one in net-snmp and new gcc.
After all macros are expanded I get in containers.h:440:

if (((void *)0) != x->container_name)
  do { 
    if (x->container_name) { 
      { 
        void *__t = ((void *)x->container_name);
        ntop_safefree((void**)&(__t),
"/usr/include/net-snmp/library/container.h", 440); 
        (void *)x->container_name = __t;
      }; 
      x->container_name=((void *)0); 
    }
  } while(0);

I do not see anything wrong at the first sight, I'll try to investigate it. The
code is perfectly compilable with gcc in Fedora 7.

The line "(void *)x->container_name = __t;" is syntactically wrong, cast (void*)
does not result in l-value, see ISO C, section 6.5.4, 

You redefine free() and you assume that the value passed there is l-value, but
net-snmp passes r-value -> compilation error. Your free() should accept r-value
instead, as usual function call.

Thanks for your very timely response.  I'll try to get that fixed.