Server Response Error:'Invalid ViewState'

[TJuly]

I have 2 Pages (Listing and Entry) using Master Page.
Firstly I am in Listing page.
When click the 'New' button in Listing Page, I go to Entry page below.
Server.Transfer("~/Job/JobCodeEntry.aspx");
In the entry page, I use User Control for Multi FileUpload.

Whenever I upload, I got this err. Help me please.

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

Best Regards,
TJuly.

[Ketsuekiame]

The quickest solution is to add the <machineKey> setting into your App.Config.

The actual (best) solution will entirely depend on how the error is ocurring, which I'm afraid is going to be a debugging task for yourself.
This error can be caused by the machine key being different on the server than the one that was used to encrypt the viewstate in the cookie.

Unfortunately, that's the best that I can offer you.

[KushMishra]

I think you can follow Ketsuekiame's approach as of now and kindly inform if that works out for you :)