error compiling freefilesync 4.5 !

[rbadillarxxx]

Hi all:
As far I know; I have installed/compiled all requesites for compiling
freefilesync 4.5 on my ubuntu 11.04 (32bits).
But after hit enter to make command I got this:
# make
if ; then mkdir OBJ; fi
if ; then mkdir OBJ/FFS_Release_GCC_Make; fi
g++ -Wall -pipe `pkg-config --cflags gtk+-2.0` -O3 -pthread -std=gnu++0x
-DNDEBUG -DwxUSE_UNICODE -DFFS_LINUX -DZEN_PLATFORM_OTHER
-DWXINTL_NO_GETTEXT_MACRO -I. -include "zen/i18n.h" `wx-config --cxxflags
--debug=no --unicode=yes` `pkg-config --cflags gtkmm-2.4` `pkg-config --cflags
unity` -DHAVE_UBUNTU_UNITY -c algorithm.cpp -o
OBJ/FFS_Release_GCC_Make/algorithm.o
algorithm.cpp: In function ‘std::pair<DataSetDir, const zen::DirContainer*>
retrieveDataSetDir(const Zstring&, const zen::DirContainer*)’:
algorithm.cpp:395:41: error: ‘nullptr’ was not declared in this scope
algorithm.cpp:396:1: warning: control reaches end of non-void function
make: *** Error 1

any idea to get rid of this error?!

TIA

[Zenju]

The recent versions of FreeFileSync require GCC 4.6.1 which is shipped with
Ubuntu 11.10.