The specified server cannot perform the requested operation

we have 40 systems ,most of systems only 2000 pro only.but some systems only netbios serives not working the following error showing : the specified server cannot perform the requested operation.but if i ping that system’s,it’s ping (reply coming).pls help to me?.this issue is only in lan.there is no domain controller or group policy,its is only workgroup based.

some times following error also showing: A Specified Authentication package is unknown