Object reference not set to an instance of an object.

[Carlos Vazquez]

I developed a web page (three layer) but when i try the webpage with multiple
users it start sending this error, the error is in diferent places every time
but the error says the same thing "Object reference not set to an instance of
an object." or "Integrated Security=SSPI;Persist Security Info=False;Initial
Catalog=kdd2;Data Source=cvazquezwxp Timeout expired. The timeout period
elapsed prior to completion of the operation or the server is not responding.
"

I've already check the open and close connections and every open has the
close.

Can you help to find the error?

Thanks a lot.