import error undefined symbol: PyUnicodeUCS2_Decode

I'm trying to port a Python app from Ubuntu to CentOS 5.5. When I try to import psycopg2, I get this:

ImportError: /usr/lib/python2.6/site-packages/psycopg2/_psycopg.so: undefined symbol: PyUnicodeUCS2_Decode

My code is built against python 2.6 and python 2.6 is installed on the CentOS machine, but it's not the default Python. (CentOS becomes very unhappy if I try to make 2.6 the default.)

I downloaded and extracted psycopg2 version 2.4.4 from http://initd.org/psycopg/download/and have performed the following steps:

python26 setup.py build
python26 setup.py install

Hoping to get lucky, I replaced the _psycopg2.so file on the CentOS box with the _psycopg2 from my (working) Ubuntu machine. That just got me another error:

ImportError: can't import mx.DateTime module

Python 2.6 seems to have been compiled with UCS4, and I am building
psycopg2 against 2.6, but when I do that it still seems to be looking for a UCS2 symbol.

Am I missing a step somewhere?