error (Urgent)

this is going very wrong, it comes from nothing

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.

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: 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.

what should I do to not occur?

Thanks!

any solution?

Hi, I faced with the same problem. But unfortunatelly I dont have enuough time to look deeper in it. You can look at this page. It might help you:
http://forums.asp.net/t/955145.aspx?PageIndex=9

BTW, I usually do the following steps to reproduce this issue:
Quikly select different currencies in combobox in a public store. I supose that the problem is because of AJAX.