OpenERP starts more than one process to handle multiple requests from multiple web clients and to run OpenERP cron jobs while simultaneously serving web clients. OpenERP v7, uses MultiCorn, and v6 uses Gnuicorn (both are WSGI compliant web servers) to pre fork the OpenERP processes. This improves performance on multi core servers. The number of worker process can specified by the following settings:

/etc/openerp-server.conf worker = [number of workers]

command line: --workers=[WORKERS] Specify the number of workers, 0 disable prefork mode

There should only be one, unless you are purposely running multiple OpenERP server processes.

Perhaps two of them have crashed?