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This article explains why you get an error message when downloading content from Content Store.
Read more about downloading content from Content Store in this article.
About the error message
When downloading content from Content Store as an Excel file, you may get a notification explaining that a job is already in progress and an email saying "An error occurred when managing your Content Store cart for [your content store]. If the error persists, contact your system administrator.".
An error is also logged in the Control Center log. Read more about Logs in this article.
This happens when a download job is triggered while another download job is already running. This is because the jobs are not queued.
You need to wait for a Content Store download job to finish before starting a new one.