problem on validating aspx pages

[Mr. x]

Hello,
I don't know whether this is a bug on the .NET server side,
but for the link : http://www.moca.co.il/main/main_contact.aspx
by checking with http://validator.w3.org,
I found that the code that is automatically generate by the .NET server (for
my *.aspx file) - there is an error on my page :

...."_ctl0" method="post" action="main_contact.aspx" id="_ctl0">
(If you validate the link I gave, you'll see the problem).

Is there something I can do that I won't get that error ?
Should I ignore that error ?

Thanks