This problem was encountered when calling a function (using gdb.parse_and_eval()) in a Python inferior that returns a PyObject *. This is the result of a debug session with Pdb (the Python Debugger) inside gdb:

(Pdb) print gdbval
<unknown at remote 0x-80f8220>
(Pdb) print gdbval.address
None
(Pdb) long(gdbval)
-135234080L
(Pdb) print gdbval.type
PyObject *

As you can see, the address is negative when you print the value or try to convert it to a Python long.