Cant Login with POST

[Alberto]

I need to login to:
http://www.bolsar.com/net/principal/contenido.aspx
Usuario (User): IRSA   Clave (password): 4752075

I run Fiddler

With FB
I get the page, the GET in fiddler shows the cookies (ASP.NET_SessionId)
Write User and Pass in FB, press "Entrar" (Login), the POST in fiddler shows the same cookies and the following post string:

__EVENTTARGET=&__EVENTARGUMENT=&__VIEWSTATECOMPRIMIDO=xxx&__VIEWSTATE=&keyword=&_ctl10%3AtxtUsuario=IRSA&_ctl10%3AtxtPassword=4752075&_ctl10%3AimbEntrar.x=16&_ctl10%3AimbEntrar.y=8&quick=&buscarSociedad=

It logs in ok.
VIEWSTATECOMPRIMIDO=xxx , xxx is a very long string


With the DEMO app
Goto the Web Client
Web Page/Address tabs, write the URL and press "Go Fetch"
From Fiddler I read the GET and locate the Cookies:

ASP.NET_SessionId=haiu2c45v2a03m55h451e255;CS_Ultimo_URL=http://www.bolsar.com/net/principal/contenido.aspx;

Goto the cookies Tab and write it

Goto the Generic Post Tab, write the URL and the following Post String:

__EVENTTARGET=&__EVENTARGUMENT=&__VIEWSTATECOMPRIMIDO=&__VIEWSTATE=&keyword=&_ctl10%3AtxtUsuario=IRSA&_ctl10%3AtxtPassword=4752075&_ctl10%3AimbEntrar.x=30&_ctl10%3AimbEntrar.y=9&quick=&buscarSociedad=

I dont know how to post in the VIEWSTATECOMPRIMIDO, then I leave it blanked

I press the POST button and get a:

Specified cast is not valid.
Server Error in '/NET' Application.
....... etc etc

If I try with the following post string:

_ctl10%3AtxtUsuario=IRSA&_ctl10%3AtxtPassword=4752075&_ctl10%3AimbEntrar.x=30&_ctl10%3AimbEntrar.y=9&quick=&buscarSociedad=

I get no error but It does not logged in
How can you realize you are not logged in? because if you go down 4 pages in the Return data text field you will see the words: "Usuario" and "Clave" which means you are in the original page without logged in. If you logged in succesfully you would see a "Usuario logueado:" string

How can I do it?
May be I need to send the VIEWSTATE, but how to know it?

Thanks
Alberto

[Alberto]

I could sort it out.