Shared Memory: out of memory

Hello,

I'm working with the JDBC driver from the Postgresql 7.0.2 distribution.

My application creates transactions consisting of about 3000
updates operations ('insert into table' and 'create table').
My database consists of a huge (200000) number of tables which
form a hierarchy.

The postmaster throws the following error massage

>NOTICE: ShmemAlloc: out of memory
>FATAL 1: LockAcquire: lock table 1 is corrupted

What can have caused this error? How can I overcome it?
Should I define the parameter -B of the postmaster?

Thank you in advance
Sofia Alexaki