there was a data source access error. please contact the gateway administrator

Hi rayudu,

Firstly ensure that your SSAS server and gateway are installed in a same domain or trusted domains.

Secondly, in Power BI,  the effective username is passed to the gateway and then onto your on-premises Analysis Services server each time a user interacts a report connected to Analysis Services. The email address that you use to sign in Power BI with is passed to Analysis Services as the effective user. This email address should match a defined UPN within the local Active Directory Domain, if a match cannot be found, you will get errors.

You can use the following command from your workstation to find out the UPN for your account, if the UPN doesn't match the email address you sign into Power BI with, you can use “Map user names” feature to solve this issue.  Assume that you if you sign into Power BI with [email protected], but your local directory UPN is [email protected], you can configure a mapping rule to have [email protected] passed to Analysis Services. For more details, please review this article.

whoami /upn

Thanks,
Lydia Zhang