Reg: SQL Query for Postgres 8.4.3

Hi,

Can any one tell me whats the effect of the below Query

SELECT substring(B'1111000000000001' from 5 for -2);
SELECT substring(B'1111000000000001' from 4 for -3);

its observed that there's an Error "invalid memory alloc request size
4244635647"

What will actually happen to the Postgresql database.

I am using Postgresql 8.4.3 on Ubuntu 8.04

Thanks in Advance
Regards,
Srinivas Naik