Hi Anand,
This is happens due to the network problem not a SAP Business One problem.
1.Check all the applications which are running on same network.(if possible reduce those applications)
2.It is better to provide one server to the Business one.
3.Always run Business one client as Administrator.
4.Check weather the clients systems is in one network or more networks.(Put the client and server in same network in adapter settings)
thank and regards
D.Rajesh