Is there a way to reduce the size of the Viewstate? When using <form
runat="server">, I want the functionality that using Viewstate gives me,
but does it have to be that large it often is? The size is 40000
characters (and that will slow down the speed of the site, I think?)!

Is there any way to reduce the size?

Depending on what functionality you need. You can disable viewstate  on a "per
control" basis by setting controlname.EnableViewState = false

If you would just like the postback functionality for a form  you can override
viewstate all together.
Then you don't even need to user a server side form.
NOTE: this has odd side effects. Like HtmlInputImages cannot raise the
ServerClick event.

C# code

protected override object LoadPageStateFromPersistenceMedium()
{
return null;
}
protected override NameValueCollection DeterminePostBackMode()
{
if(Request.Form.Count > 0)
{
return Request.Form;
}
return null;
}
protected override void SavePageStateToPersistenceMedium(object viewState)
{
// Do nothing.
}

yes, turn it off...

viewstate=off

I have now turned it off by writing

<%@ Page EnableViewState="false" %>

on the top of the page, and the viewstate  was really reduced ;-)

But there is one thing that confuses me:

I have a form  with some fields. After posting the form, it still
remembers the content of the fields. Why is the content remembered when
the viewstate is turned off?

Form submission and Viewstate are 2 different things.
Viewstate is Microsoft's attempt at remembering data
that is in the form  Inputs so when you come back after
submitting the form, it still keeps whatever was
input.

Pretty bare bones explanation that someone else on
this list could expound on or alter to be more
precise.

When i try to view my aspx page i get the following error:
The viewstate  is invalid for this page and might be corrupted.
What could cause it? I had the same error a few days ago with a different page
but after restarting the computer i was able to view my page. This time however
i can't view my page.

support.microsoft.com/default.aspx?kbid=323744
has something to say about this error. Look for other
fixes on microsoft.com.

you can try enableviewsatemac=false at the page directives .
This may solve your problem

I get the following error:
The 'enableviewsatemac' attribute is not supported by the 'page' directive.

ok i managed to do the enableviewstate thingy :-) but i still get
The viewstate  is invalid for this page and might be corrupted.
Description: An unhandled exception occurred during the execution of the current
web request. Please review the stack trace for more information about the error
and where it originated in the code.

Exception Details: System.Web.HttpException: The viewstate is invalid for this
page and might be corrupted.

Source Error:

An unhandled exception was generated during the execution of the current
web request. Information regarding the origin and location of the exception can
be identified using the exception stack trace below.

Stack Trace:

[HttpException (0x80004005): The viewstate is invalid for this page and might be
corrupted.]
System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +150
System.Web.UI.Page.LoadPageViewState() +18
System.Web.UI.Page.ProcessRequestMain() +423

Four alternatives i can think of (the fourth one may
be a bit drastic, but you never know) :-

1) Search the archives of this list for the error, and
take some action.
2) Search microsoft.com for the error.
3) Try repairing the .NET installation
4) Remove and re-install the .NET installation.

I get to the page that gives me the problems from a previous page-nav.aspx that
only has buttons and each button is directed to a different page. All the other
pages work fine only one page -payads.aspx gives me the viewstate  problem.
When i change the buttons onclick from
btnAds2Pay.Attributes.Add("onclick", "SbtForm ('payads'); return false;")

to:

Private Sub btnAds2Pay_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnAds2Pay.Click

Server.Transfer("payads.aspx?aprst=1")

End Sub