Error TCP/IP ENCONNRESET

Has anyone seen the following message?

Error TCP/IP ENCONNRESET

When I finish the number of logons granted from the licence, I control if there are inactive users connected from more than n° minutes, and I disconnect them; When I do it, I have the error message, and I must reboot the server.
I’m sure that the problem isn’t in the network adapter.
I use Navision 4.0, the SO on the server is Windows 2003.

Does anybody help me in this case.

Thanks in advance.
Angela