another question regarding web application

is it the timer won't work in web form? because i had tried it but seems like the timer never fire an event. Besides that, do we have any particular rules in using the thread inside the web form? because i have facing a problem in using the thread inside the web form. the situation is i hava create a thread and i use the debug to monitor it and i found that when the thread loop for second time it will cause an error! do someone can give me some guideline on this cause i just a beginner of Microsoft VB.NET