Connections dropped randomly

I find that if I reuse a jdbc connection to perform a number of
update queries (e.g. 1000), the connection keeps getting dropped
after a random number of iterations.

This occurs in all sorts of queries throughout my application.  Any
idea what might be causing this?  I'm not doing anything
out-of-the-ordinary, and it happens on both prepared statements
and regular statements.

I had this problem in postgres 7.3, and it's still there after
upgrading to 7.4.4 & pg74.215.jdbc2.jar.

Thanks,

-Mike