Asp.net Validation of viewstate MAC failed -

i receiving following error @ times on asp.net website.

 sys.webforms.pagerequestmanagerservererrorexception:   validation of viewstate mac failed.   if application hosted web farm or cluster,  ensure <machinekey> configuration specifies   same validationkey , validation algorithm.   autogenerate cannot used in cluster. 

when page refresh goes,no problem.how can solve problem?

if you're using web farm , running same application on multiple computers, need define machine key explicitly in machine.config file:

<machinekey validationkey="jfdsgoieurtjktrekoiruwtklrjtkuroiuflksiosugoifds..." decryptionkey="kajdfoiauoilker534095u43098435h43oi5098479854" validation="sha1" /> 

put under <system.web> tag.

the autogenerate machine code can not used. generate own machinekey see powershell script: https://support.microsoft.com/en-us/kb/2915218#bookmark-appendixa