Problems allocating more memory

Here is the error I'm getting:


> 001105.14:42:28.236  [1124] IpcMemoryCreate: shmget failed (Invalid
> argument) key=5432001, size=286224384, permission=600
> This type of error is usually caused by an improper
> shared memory or System V IPC semaphore configuration.
> For more information, see the FAQ and platform-specific
> FAQ's in the source directory pgsql/doc or on our
> web site at http://www.postgresql.org.
> 001105.14:42:28.237  [1124] FATAL 1:  ShmemCreate: cannot create region

I have re-compiled my kernel and increased SHMMAX.  Are there some other memory settings I should be making?

I am running Red Hat 7.0 with all patches.

All help appreciated.

Chris.