Sorry for the previous corrupted reply.
======================================
Hello Russell,
Yes, I think Bruce's explanation and suggestion is reasonable.
The reason you'll get such error when you postback a page that has been
idle at client for a long period is as below:
ASP.NET web page use ViewState to store some persisted states and info of
webcontrols on the page. And this is stored in a <input name="__VIEWSTATE"
..../ html hidden element. And since this data is sensitive, ASP.NET by
default enable the ViewStateMac for every page. This ViewStateMAC is like a
simple digest&signatuer of the ViewState append in the Viewstate and
whenever postback, the ASP.NET runtime will verify the viewstate(with the
digest signature) to see whether it is tampered or not.
The digest&signature of Viewstate is generated based on a validationkey,
this key is bydefault autogenerated and will vary between different
applications or before and after application restart. Therefore, when the
user request a page and let it idle at client-side for a long period, if
the web application at server-side has restart(appdomain recycle or process
recycle), the validationkey(used to generate viewstate MAC) will be
changed, thus, if you postback with the old viewstate & MAC, the
server-side runtime will fail to verify it and report ViewState validation
error. You will also encounter such problem when you visit a page from
google's cache image(with invalid viewsate content it it).
Bruce's suggestion is that you can manually specify the validation key in
the machine.config or application's web.config so that the ASP.NET runtime
will always use the fixed key to generate the ViewState MAC(no matter the
application has restarted or not). And in webfarm environment you can event
make different applications on different server use the same key.
Here is a good article detailedly describe how to generate a custom Key and
specify it in the web.config file:
#How To: Configure MachineKey in ASP.NET 2.0
http://msdn.microsoft.com/library/en...7.asp?frame=tr
ue
Hope this help clarify some. If you have anything unclear, please feel free
to post here.
Sincerely,
Steven Cheng
Microsoft MSDN Online Support Lead
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