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
As I found out, there was a
tag in header part of my master page, that I added in last tie and before publishing. This tag specify a default URL and a default target for all links on a page. This was the main cause of the fault, this time.
I hope that it will help others too.