For a system that was working fine and now is not, the first rule/question is "What was changed?"
When was the last time one of the servers involved was rebooted?
Is this a 100 Mb switched network? If so, are all the adapters and ports set to 100/FULL duplex explicitly. It has been a known problem for years that "Auto Negotiate" does not work as intended in a 100 Mb network.
Did someone change any of the programs? If so, they probably introduced the problem.
Has the database software been upgraded? Does it then need to be retuned?
Has SAS been upgraded? Does it then need to be retuned?
Is there now a bottleneck in the network due to the addition of other traffic?