That error means you are trying to connect one more process to your database than is allowed as defined by the -n startup parameter.
Log onto the box and enter into the Progress environment. Do a proshut dbname. You will then see all the connected processes (user logins, brokers, writers, report builder runs, etc.). You may see a buch of "rogue" processes in that list. In which case, you can shut them down from the proshut utility. If all processes are normal, then you'll need to increase the value of the -n when the database is started (proserve dbname -N tcp -H hostname -S service -n 20).
HTH
-Dan
