Can't connect to 6.5.2 server with 7.0.2 client

I was just about to give postgres 7.0.2 a try on my development machine,
but after installing it, I find that I can't connect to my 6.5.2
production servers.  The following error message is reported by both psql
and pgaccess, upon trying to connect:

ERROR:  MultiByte strings (MB) must be enabled to use this function

The connection then fails.  Is there some way around this, short of
upgrading all my production servers?

Cheers,

Forest