Thank you for posting in Microsoft Q&A forum.
The error message means: The report server is unable to decrypt and use any data that is encrypted with the current key.
You may refer below articles to get the appropriate solution:
https://businesswintelligence.com/content/64/ssrs-pbirs-encryption-key-integrity
(Please Note: Since the website is not hosted by Microsoft, just for your reference.)
https://social.technet.microsoft.com/wiki/contents/articles/52585.ssrs-troubleshooting-the-report-server-was-unable-to-validate-the-integrity-of-encrypted-data-in-the-database.aspx
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.