Could not send Query(connection dead)

My client application receives this error randomnly a number of times per
day when user tries to save document.

TCP connection to server seems to be OK since

INSERT INTO logfile ...

command which logs this error to database works.
(I use singe TCP connection to server in applicaton).

How to fix this error ?

Environment:

Postgres 8.1.3 running in Windows 2000 server

Client application uses Postgres ODBC driver from XP, no SSL

Andrus.