Problem connecting to Postgres

I used pgadmin a while ago with no problems at all - a very useful tool! After one of the upgrades I now cannot connect to my postgres server (which runs on a spearate Linux box). When I try to connect I get an error message from pgadmin:
An error has occured in pgAdminII:frmConnect_Click
Number: -2147467259

On the Linux console I get:
ERROR: Function: 'pg_client_encoding()' does not exist
Unable to identify a function that satisfies the given argument types
You may need to add explicit typecasts

My PC is running Windows 2000
The Linux box is running:
RedHat Linux 7.3
PostgreSQL 7.2.3 - Installed from the standard RPMs

I'm not in a position to upgrade to PostgreSQL 7.3 at this stage.

I've been installing some of the older releases to see when this problem was introduced (and to make sure it's not my database!)
version 1.2.0 : Works fine.
version 1.3.60 : Fails with the error described above
so looks like a problem from version 1.3 onwards.

Any help greatly appreciated!
Peter Wilson