It seems that smartnav conflict with webUIValidation:

Build a web form with one text box and 1 button, the textbox link to a 
required validation control. click the button to redirect to another 
page.

set smartnavigation=3Dtrue
scenario A
start this page, enter some chars in textbox, click button, a new page 
will be shown correctly.

scenario B
1. start this page, and click button, required validation control works 
and give a message something like the text box cannot be empty.
2. now type in some chars in text box, then click button, this time the 
button does not work, it does not redirect to another page.

However, if set smartnavigation=3Dfalse, the above 2 scenario are all 
working fine.

Very much appreciate if anyone can help to solve such problems because I 
have no choice to use smartnavigation for very long page.

Regards,