FATAL: invalid frontend message type 47 server closed the connection unexpectedly

I receive this message when I do a specific operation.
How can I debug something like this?

I use a Centos 4.0 distribution, postgresql version 8.1.3(I also used
diffrent distibutions and other versions of postgresql).
I connect to postgresql using perl DBD::Pg, using a tcp socket.

The error appears when I do a specific operation, but if I try many
times, it will work.
It works only if I try many times and fast.