Hi Mat, thanks for your advice. Supposely the SQL is just a very simple query and normally it just take about 2 seconds to login, I'm just curious why it will exceed the default timeout setting, and this only happens to 1 of my client and not others.

The application was working fine in last two weeks, and the problem just started few days ago. Whenever this problem occurs, restarting the SQL service will resolve the problem, but it will just happen again after sometimes. I read some articles mentioned that the pooling does matter, any idea? Thanks.