Error: Unable to upgrade port: 1

[eli li]

For some reason I'm not able to update the mac ports. The error is:

/usr/bin/g++-4.2 -c -pipe -isysroot /Developer/SDKs/MacOSX10.6.sdk -arch i386 
-arch x86_64 -O2 -Wall -W  -I../../../mkspecs/macx-g++ -I. -o libmng.o 
libmng.cpp
/usr/bin/g++-4.2 -headerpad_max_install_names -o libmng libmng.o     
-Wl,-syslibroot,/Developer/SDKs/MacOSX10.6.sdk -arch i386 -arch x86_64 -lmng 
ld: warning: in /opt/local/lib/libmng.dylib, file was built for unsupported file 
format which is not the architecture being linked (i386)
Undefined symbols for architecture i386:
  "_mng_cleanup", referenced from:
      _main in libmng.o
ld: symbol(s) not found for architecture i386

Unfortunately, uncle google says nothing about this problem.