I was getting this error using
FormsAuthenticationTicket ticket =
.I was trying Forms authentication to pass encrypted ticket between two web applications.I left out
This configuration means to create different key for each web applications thus it failed as
encrypted key was not same in two web applications.
so how to get same key for forms authentication. I resolved this issue by setting static values in section in both web.config files.
<machineKey validationKey='B5D752F96C1196D2A98014A3EF96F35192183FA47D467ACF0969F3687EC3C6BA3A959CD85BD3C282F2390B220ACD742568A8BC36BDBFBF9306ED807E6B090D56' decryptionKey='4BE38697FCD33A2C61D8FC93754FA668CEE4B5467B6B81F6' validation='SHA1'/>
Validation and decryption were generated using online machinekey generator tool.