Hi,
Based on the description, it seems the problem is more related with SQL. Have you gone through the steps mentioned in the below post?
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/613a33f4-4a8d-4b38-8679-049ab0137c17/an-impersonation-error-occurred-using-the-security-context-of-the-current-user-report-server-is?forum=sqlreportingservices
Alex
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