Hi @Sravanthi G ,
This error usually refers to a configuration issue within the SQL Server Reporting Services (SSRS), I would check the unattended execution account that it is configured properly, have a look through the following links:
How to Manage the Report Server Unattended Execution Account in Operations Manager
https://learn.microsoft.com/en-us/system-center/scom/how-to-manage-the-report-server-unattended-execution-account?view=sc-om-2019
Configure the Unattended Execution Account (Report Server Configuration Manager)
https://learn.microsoft.com/en-us/sql/reporting-services/install-windows/configure-the-unattended-execution-account-ssrs-configuration-manager?redirectedfrom=MSDN&view=sql-server-ver15
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Best regards,
Leon