Is this a new installation or an upgrade? Was this working before and suddenly stopped or is this a new issue?
My first thought would be permissions - are you sure the computer running Tableau Server has access to the data source? The Run As User account needs permission to reach that resource. If the user on Tableau Desktop has no issues but Tableau Server does, that likely points to a problem with permissions. You can test by installing a copy of Tableau Desktop on the computer running Tableau Server and attempt to access the data from there. If that is unsuccessful - it is almost assuredly a problem with RAU permissions.
Community entry on failing extracts: Server Extract Failed to Refresh
RAU Account Permissions: Required Run As User Account Settings
Thanks and hope this helps!