When you look in Event Viewer, are you looking at all three logs? There should be something in there to give us a clue. The system log is probably where we should see a problem, but the application and security logs could shed some light. Once in Event Viewer too, check your Log Settings by clicking on "Log" and "Log Settings" and up the Maximum log size to 1024 and check "Overwrite as needed". You have to do this for each of the 3 logs. Then let's see what we get the next time this happens.
Also, describe more specifically what you mean by "the workstations will not be able to see the server" when this happens so we can best understand how you are perceiving what is happening.
Lastly for now, where does this application reside that is getting locked up?
There are so many factors and not enough specifics to really help, so we're going to need more input from you.
Before I submit...when the workstations loose the ability to see the server, open a command prompt on one of them and try to ping the server (ping servername). Then pint the server's IP address. Post that here when it happens again and it will help everyone to know the next thing to do in our troubleshooting.
Good Luck,
G