Must explicitely the ID of control? Why?

[Amelyan]

The following error occurs when I do the following:

1) Click "Back" button on my internet explorer, which brings my pre-request
page.
2) Then click on *any* control that has a handler.


"An error has occurred because a control with auto-generated id '_ctl6'
could not be located to raise a postback event. To avoid this error,
explicitly set the ID property of controls that raise postback events. "

Does anyone knows why this happens?

Thanks,

Amelyan