Can't starting postmaster with -B 512 Option

System Spec
    SUN OS 2.6
    PostgreSQL 6.3 Version

[Error Message]
sol% postmaster -B 512 -S -D /usr/local/pgsql/data
IpcMemoryCreate: memKey=5432001 , size=4501144 ,
permission=384IpcMemoryCreate: shmget(..., create, ...) failed: Invalid
argument
This type of error is usually caused by improper
shared memory or System V IPC semaphore configuration.
See the FAQ for more detailed information
FATAL 1:  ShmemCreate: cannot create region

I don't know why error occured....
Please.. Help me.....