too many connections on NT4.0 SBS

Hi. HAve mixed NT4.0 SP6 SBS server, and NT4.0 SP6 clients. Quite often a client is refused access to a shared resource, with message “there are as many connection as this server can accept”.
Actually I see no more than 5 open files, and even closing everything it takes about 10 minutes to clear resurces and grant access. How can I manage this problem, or can I determine exactly which resource is using too much resource, and how can I kill it immediately ?
Thank you. Mike