Presumably, you've checked your existing code and web.config, and tried increasign teh timeout there:
HttpSessionState.Timeout Property (System.Web.SessionState)[
^]
If that doesn't work, then you need to talk to your web hosting company: I know that some reduce it to five minutes and have set that increases beyond that are ignored, but ten seconds seems rather extreme. If it's been reduced by the web host, then only they can increase it, so if they won't cooperate, you will have to move to cookies.