directory initialized 7.2 not compatible 7.1.3

I have 3 Postgresql servers
Let's call them 1, 2 and 3
1 is the primary. Recently upgraded to 7.2
2 is the backup. Recently upgraded to 7.2
3 is the web server and basically I installed postgresql so I could
compile mod_php with postgresql support.

My upgrade went like this:
Uprade backup machine, 2, to 7.2
Point PHP scripts to use machine 2
Upgrade primary machine, 1, to 7.2
Tried to switch the PHP scripts back to using the primary machine

At that point I got an error:
Data directory was initialized by PostgreSQL version 7.2, which is not
compatible with this version 7.1.3

I thought the problem was that the web server needed to be updated to 7.2
so I did. However all along the PHP scripts were working with the backup
machine fine.

After upgrading the web server, machine 3, to 7.2 I am still having the
problem.

Summarizing: I have 3 machines which I have upgraded to 7.2, but somehow
one of them thinks that one of the machines is still 7.1.3.
I also tried to connect from psql and it gave me the same error. On the
machine been reported as having 7.1.3, machine 1, I do "select version();"
and it reports it is 7.2. Moreover looked at the PG_VERSION file and it
has 7.2 listed.

Any clues?