Question : Asp's Page ViewState

Hello,
I have an asp page the loads in a modal window in a web application, this page loads information into a treeview control, I am having a problem when I try to dismiss the modal window by calling some javascript it takes a while for the javascript to execute, I tried to disable the viewstate of the page and tried to dismiss the page things work fast, the problem is i Need the viewstate as this treeview control is interactive and if the viewstate is disabled the UI is lost.
Note that I have to actions on the page one is to dismiss modal window and the second is to do some modifcation and then dismiss, I have slow load times with both, but what I do not get is why is the page slow to dismiss although no modification were done?
Any ideas how I can make the execution faster.

Answer : Asp's Page ViewState

asp:button has an event "OnClientClick" which will not postback... u can directly call the javascript function to close the window...

its basically posting back with the huge amount of View State content and that's where its getting delayed.