Pass thru Login in a asp.net site

[Marcelo Chryssovergis]

Hello people,

I´m trying to make the authentication in a asp.net site, but without success.

An Asp.Net site generates some hidden fields like:
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" /><input 
type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" /><input 
type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" 
value="/wEWBAKstPOeBgL75ouGDgLznKRyAqOFwpwEtGJkEsfmFcRyE4LGeK8v6mZkNO0=" 
/><input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" 
value="/wEPDwULLTE2ODM2MDczMjlkZG1Ww1x8lZCXOXsQ0tkUR8hph/dO" />and the fields 
Login and Password:

<input name="ctl00$ContentInterna$txtEmail" type="text" 
id="ctl00_ContentInterna_txtEmail" class="text" />
<input name="ctl00$ContentInterna$txtSenha" type="password" 
id="ctl00_ContentInterna_txtSenha" class="text" style="width:122px;" />

I get the hidden fields dinamically and send with the login and password. But I 
aways get this error:

"Validation of viewstate MAC failed. If this application is hosted by a Web 
Farm or cluster, ensure that &lt;machineKey&gt; configuration specifies the 
same validationKey and validation algorithm. AutoGenerate cannot be used in a 
cluster."

Please, anyone can help in this one?

Thank you,

Marcelo