Server Fault is dedicated to serving a particular market: Professional system and network administrators (http://serverfault.com/about ; http://serverfault.com/help/on-topic).
From you question it's pretty evident that you're not the system administrator responsible for this environment. Wanting to know something for your own education is an admirable thing, but it does not make it an on-topic question for this site.
In this case even if you are the system administrator for the environment involved, your question doesn't meet our quality standards -- There is no evidence of research or troubleshooting, a nearly infinite set of possible causes, and so the question simply cannot be answered as asked.
We have a Q&A here on meta that discusses some things that go into making a good, answerable question, but the basic premise is that you need to do some (fairly extensive) digging on your own, and at least summarize that work so we're not going over the same ground.