Hi Patrick,
1. Both machines are running in en_US locale.
2. As far as I know, the PostgreSQL client/server protocol has not changed. The psql from the Openacs/PG 7.1.2 server is able to connect to the 6.5.3 database on the other server.
3. There are no other error messages regarding postgres. It is able to access the local openacs database just fine.
4. I compiled it myself from the pgdriver-2.0 source, using the PG 7.1.2 libraries and headers.
I'm going to try compiling a PG 6.5.3 on the openacs machine and build a second postgres driver using the 6.5.3 libraries and headers. Maybe that'll work.