sql server time out problem

The timeout belongs on the connection and/or the command. Setting it in the web.config file doesn't add anything because connections and commands aren't magic - they don't know what this value is. Now, the first thing you have to ascertain is whether it's a connection timeout, or a command timeout. In other words, is the problem because it's taking too long to connect to the database server, or is the command taking too long?

If it's connecting to the server, there are strategies such as connection pooling that can help to alleviate problems - you really need to understand your application architecture though. Make sure that you are freeing up connections so that they can be recycled to the pool and picked up from there, rather than being created from scratch every time - this is an expensive operation.

If it's a command timeout, then you could increase the timeout on the SqlCommand. I say could because command timeouts generally indicate that there's a deeper problem with the code, and an increased command timeout may mask the problem for a while, but it will be sitting there to kick you when you least expect it. If you can isolate where the exception is happening (hint - log your exceptions to get the stack trace) then you should easily be able to isolate the command that is causing the problem. When you do this, you can actually analyse the SQL that's at fault - I would use a SQL Profiler here to really figure out what's going on.