post to another page

[nik]

I have a postback on an aspx-page. In this postback I perform a
redirect. The page is quite heavy, so instead of performing a postback
I perform a post to another empty page, which then can do the
calculations necessary to perform the redirect. The post to another
page is done by changing the action property of the form clientside.
First of all: This doesn't seem like a nice solution. A bit of a hack.
Is there a better way to perform a post to another page from an aspx.
Secondly: When I hit the empty page I get an exception. I suppose it is
due to a mismatch in the viewstate information:
An uncaught exception occurred:Unable to validate data. Stacktrace:
at System.Web.Configuration.MachineKey.GetDecodedData (Byte[] buf,
Byte[] modifier, Int32 start, Int32 length, Int32& dataLength)
at System.Web.UI.LosFormatter.Deserialize(String input)

Any idea how I can solve this problem?

Another strange thing is that this exception never shows up in the
browser. It is only caught in the Global.asax method
Application_Error(...). Why is that??