Using Apache AB

Hi,

Hardware:
System Configuration: Sun Microsystems sun4u SUN 420R (4 X
UltraSPARC-II 450MHz)
System clock frequency: 113 MHz
Memory size: 4096 Megabytes

OS:
Solaris 8

Apache Build:
Server version: Apache/1.3.34 (Unix)
Server built: XXXXXXX
Server compiled with....
-D EAPI
-D EAPI_MM
-D EAPI_MM_CORE_PATH="logs/httpd.mm"
-D HAVE_MMAP
-D USE_MMAP_SCOREBOARD
-D USE_MMAP_FILES
-D HAVE_FCNTL_SERIALIZED_ACCEPT
-D HAVE_SYSVSEM_SERIALIZED_ACCEPT
-D HAVE_PTHREAD_SERIALIZED_ACCEPT
-D DYNAMIC_MODULE_LIMIT=64
-D HARD_SERVER_LIMIT=1024

I've recently started using apache ab to test connections from my
webserver to my database server. Only problem is I can't get ab to use
concurrency greater that 252. When I try it reports the following;

Copyright (c) 1996 Adam Twiss, Zeus Technology Ltd,
http://www.zeustech.net/
Copyright (c) 1998-2002 The Apache Software Foundation,
http://www.apache.org/

Benchmarking dev-syst (be patient)

Test aborted after 10 failures

: Bad file number


What have I done wrong? Can anyone recommend any other ab type tool?

Thanks

Noel