Timeout expired error. Is it because of a query or server settings?
Timeout settings are a configuration of the client connection, so are either set by the client application, or via the connection string. Look at how your applications is instantiating the database connections, or perhaps in your application config files that control how those connections are created.

But increasing the timeout is just treating the symptom. Determining why the timeout occurred is a more difficult problem, and may require some detective work. Here are some avenues of investigation:


Is the error always throwing on one or two particular queries? You might need to do some query tuning.
Is the error always occurring at the same time each hour? Does that correspond to maintenance running overnight, perhaps in scheduled SQL agent jobs?
You might run SQL trace/profiler overnight, filtered by query duration, to see if you can better identify these long-running queries.